get Firebase database

I am trying to get and show my data from the firebase database to the HTML page in a table form, but no output showing. I attached a screenshot of my database below. I have been trying for like days and can’t solve it. Can someone help me to point out what my problem is? For security purposes, I erased the details of my firebase configuration there.

    <body>

        <table>
            <thead>
                <th>Sno</th>
                <th>First Name</th>
                <th>Second Name</th>
                <th>Email</th>
                <th>LastLogin</th>
                <th>Confirm Password</th>

            </thead>
            <tbody id="tbody1">
        
            </tbody>
        </table>
        <script src="https://www.gstatic.com/firebasejs/8.6.8/firebase-app.js"></script>
        <script src="https://www.gstatic.com/firebasejs/8.6.8/firebase-auth.js"></script>
        <script src="https://www.gstatic.com/firebasejs/8.6.8/firebase-database.js"></script>

        <script id="MainScript">

                    var firebaseConfig = {
                    apiKey: "",
                    authDomain: "",
                    projectId: "",
                    storageBucket: "",
                    messagingSenderId: "",
                    appId: "",
                    measurementId: ""
                    };

                    firebase.initializeApp(firebaseConfig);

        
//---------------------GET ALL DATA-------------------------------//

        function SelectAllData(){
            firebase.database().ref('admins').once('value',
            function(AllRecords){
                AllRecords.forEach(
                    function(CurrentRecord){
                        var firstName = CurrentRecord.val().first_name;
                        var secondName = CurrentRecord.val().second_name;
                        var  email= CurrentRecord.val().email;
                        var lastLogin = CurrentRecord.val().last_login;
                        var conpassword = CurrentRecord.val().confirm_password;
                        AddItemsToTable(firstName,secondName,email,lastLogin,conpassword);
                    }
                );
            });
        }

        window.onload = SelectAllData;
//------------------filling the table-------------------//
        var stdNo = 0;
        function AddItemsToTable(firstName,secondName,email,lastLogin,conpassword){
            var tbody = document.getElementById('tbody1');
            var trow = document.createElementById('tr');
            var td1 = document.createElementById('td');
            var td2 = document.createElementById('td');
            var td3 = document.createElementById('td');
            var td4 = document.createElementById('td');
            var td5 = document.createElementById('td');
            var td6 = document.createElementById('td');

            td1.innerHTML= ++stdNo;
            td2.innerHTML= firstName;
            td3.innerHTML= secondName;
            td4.innerHTML= email;
            td5.innerHTML= lastLogin;
            td6.innerHTML= conpassword;

            trow.appendChild(td1); 
            trow.appendChild(td2); 
            trow.appendChild(td3); 
            trow.appendChild(td4); 
            trow.appendChild(td5);
            trow.appendChild(td6);
            


            tbody.appendChild(trow);
            
        }

    </script>
    </body>

enter image description here

The way I pushed the data into database

// Set up our register function
  function register () {
    // Get all our input fields
    email = document.getElementById('email').value
    password = document.getElementById('password').value
    first_name = document.getElementById('first_name').value
    second_name = document.getElementById('second_name').value
    confirm_password = document.getElementById('confirm_password').value
  
    // Validate input fields
    if (validate_email(email) == false || validate_password(password) == false) {
      alert('Email or Password is Outta Line!!')
      return
      // Don't continue running the code
    }
    if (validate_field(first_name) == false || validate_field(second_name) == false || validate_field(confirm_password) == false) {
      alert('One or More Extra Fields is Outta Line!!')
      return
    }
   
    // Move on with Auth
    auth.createUserWithEmailAndPassword(email, password)
    .then(function() {
      // Declare admin variable
      var user = auth.currentUser
  
      // Add this admin to Firebase Database
      var database_ref = database.ref()
  
      // Create Admin data
      var user_data = {
        email : email,
        first_name : first_name,
        second_name : second_name,
        confirm_password : confirm_password,
        last_login : Date.now()
      }
  
      // Push to Firebase Database
      database_ref.child('admins/' + user.uid).set(user_data)
  
      // DOne
      alert('Admin Account Created!!')
      window.location = "login.html";
      
    })
    .catch(function(error) {
      // Firebase will use this to alert of its errors
      var error_code = error.code
      var error_message = error.message
  
      alert(error_message)
    });
    

}