How to make the login page connected with both admin table and user table without defining the user type/role upon registration?

I have created a form that can be navigated between login and register user. I created one table in database using mysql for admin with one record only and multiple records for user table, so if for example I followed the method where user select his role (admin/user) upon login, then it is also easy for new users when they register new account, to define themselves as admin upon registration, how to make the login process using 2 tables admin and users from the same login form?

login.php

<?php
session_start();
$conn = mysqli_connect("localhost", "root", "", "finalproject") or die("<script>alert('Connection Failed.')</script>");

if (isset($_POST['submit'])) {
    $username = mysqli_real_escape_string($conn, $_POST['username']);
    $password = md5($_POST['password']);
    $user_type = $_POST['user_type'];

    $select = "SELECT * FROM users where username='$username' and password='$password'";

    $result = mysqli_query($conn, $select);

    if (mysqli_num_rows($query_run) > 0) {
        $row = mysqli_fetch_array($result);

        if ($row['user_type'] == 'admin') {

            $_SESSION['admin_name'] = $row['name'];
            header('location:admin_page.php');
        } else if ($row['user_type'] == 'user') {

            $_SESSION['user_name'] = $row['name'];
            header('location:user_page.php');
        } else {
            $error[] = 'incorrect email or password!';
        }
    }
};
?>

<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">


    <link rel="stylesheet" type="text/css" href="style.css">

    <title>Login</title>
</head>

<body>
    <div class="container">
        <form action="" method="POST" class="login-email">
            <?php
            if (isset($error)) {
                foreach ($error as $error) {
                    echo '<span class="error-msg">' . $error . '</span>';
                };
            };
            ?>
            <p class="login-text" style="font-size: 2rem; font-weight: 800;">Login</p>
            <div class="input-group">
                <input type="text" name="username" value="" required>
            </div>
            <div class="input-group">
                <input type="password" name="password" value="" required>
            </div>
            <div class="input-group">
                <button name="submit" class="btn">Login</button>
            </div>
            <p class="login-register-text">Don't have an account? <a href="register.html">Register Here</a>.</p>
        </form>
    </div>
</body>

</html>

register.php

<?php 

$conn = mysqli_connect("localhost", "root", "", "finalproject") or die ("<script>alert('Connection Failed.')</script>");

if (isset($_POST['submit'])) {
    $username = $_POST['username'];
    $full_name = $_POST['full_name'];
    $email = $_POST['email'];
    $password = $_POST['password'];
    $cpassword = $_POST['cpassword'];
    $phone_number = $_POST['phone_number'];
    $work_duration = $_POST['work_duration'];
    $ig_account = $_POST['ig_account'];
    $state = $_POST["state"];
    $postcode = $_POST['postcode'];
    $city = $_POST['city'];
    $gender = $_POST['gender'];
    $age = $_POST['age'];

    if ($password == $cpassword) {
        $sql = "SELECT * FROM users WHERE email='$email'";
        $result = mysqli_query($conn, $sql);
        if (!$result->num_rows > 0) {
            $sql = "INSERT INTO users VALUES ('$username','$full_name', '$email', '$password', '$phone_number', '$work_duration', '$ig_account', '$state', '$postcode', '$city', '$gender', '$age')";
            $result = mysqli_query($conn, $sql);
            if ($result) {
                echo "<script>alert('Wow! User Registration Completed.')</script> " ;
                header("Location: successregister.html");
                $username = "";
                $full_name = "";
                $email = "";
                $_POST['password'] = "";
                $_POST['cpassword'] = "";
                $phone_number = "";
                $work_duration = "";
                $ig_account = "";
                $state = "";
                $postcode = "";
                $city = "";
                $gender = "";
                $age = "";
                
            } 
            else {
                echo "<script>alert('Woops! Something Wrong Went.')</script>";
                echo $wrong = mysqli_error($conn);
            }
        } else {
            echo "<script>alert('Woops! Email Already Exists.')</script>";
            echo $wrong = mysqli_error($conn);
        }
        
    } else {
        echo "<script>alert('Password Not Matched.')</script>";
        echo $wrong = mysqli_error($conn);
    }
}

else
    echo "<script>alert('No session exist or session is expired. Please log in again')</script>";

?>


<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">

    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css">

    <link rel="stylesheet" type="text/css" href="style.css">

    <title>Registeration</title>
</head>
<body>
    <div class="container">
        <form action="process.php" method="POST" class="login-email">
            <p class="login-text" style="font-size: 2rem; font-weight: 800;">Register</p>

            <div class="input-group" style="margin-bottom: 40px;">
            Username:<input type="text" name="username" value="" required></input>
            </div>
            <div class="input-group" style="margin-bottom: 40px;">Full Name:
                <input type="text" name="full_name" value="" required>
            </div>
            <div class="input-group" style="margin-bottom: 40px;">Email:
                <input type="email" name="email" value="" required>
            </div>
            <div class="input-group" style="margin-bottom: 40px;">Password:
                <input type="password" name="password" value="" required>
            </div>
            <div class="input-group" style="margin-bottom: 40px;">Confirm Password:
                <input type="password" name="cpassword" value="" required>
            </div>
            <div class="input-group" style="margin-bottom: 40px;">Age:
                <input type="text" name="age" value="" required>
            </div>
            <div style="margin-top: 40px; margin-bottom: 20px;">Gender:   
                <label for="f-option" class="l-radio">
                    <input type="radio" name="gender" tabindex="1" value="Male" style="margin-left:10px;">
                    <span>  Male</span>
                    <input type="radio" name="gender" tabindex="2" value="Female" style="margin-left:20px;">
                    <span>  Female</span>
            </div>
            <div class="input-group" style="margin-bottom: 40px;">Phone Number:
                <input type="text" name="phone_number" value="" required>
            </div>
            <div class="input-group" style="margin-bottom: 40px;">Work Duration:
                <input type="text" name="work_duration" value="" required>
            </div>
            <div class="input-group" style="margin-bottom: 40px;">IG Account:
                <input type="text" name="ig_account" value="" required>
            </div>
            <div class="form-group" style="margin-bottom: 10px;">
                <label >State:</label>
                <select name="state" class="form-control" required>
                <option value="1">option 1</option>
                <option value="2">option 2</option>
                <option value="3">option 3</option>
                </select>
            </div>
            <div class="input-group" style="margin-bottom: 40px;">Postcode:
                <input type="text" name="postcode" value="" required>
            </div>
            <div class="input-group" style="margin-bottom: 50px;">City:
                <input type="text" name="city" value="" required>
            </div>
            <div class="input-group" style="margin-top:40px;">
                <button name="submit" class="btn">Register</button>
            </div>
            <p class="login-register-text">Have an account? <a href="login.php">Login Here</a>.</p>
        </form>
    </div>
</body>
</html> ?>