How can I add a replace for a br in a .php-file? [closed]

Here is my .php-file:
index.php:

<html lang="sv-gibraltar">
   <head>
      <title>Eliseshundar.se&reg;</title>
      <meta charset="utf-8">
      <link rel="stylesheet" href="/reset.css">
      <link rel="stylesheet" href="/https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
   </head>
   <body>
      <?php echo "<table class='table'>";
         echo "t";
         echo "<td class='tableSub'>";
         echo "<br>";
      ?>
      PLEASE REGISTER AN ACCOUNT HERE
      <!-- Here I have entered a simple registration form, without credentials. -->
      <script src="Array.js"></script>
...

And here is the JS-file:
Array.js:)

// Squeeky clean files go everywhere!
this.HTMLTableCaptionElement
// Here I have selected, a null table
this.table = "";
this.table.trimEnd.querySelector('.tableSub');
this.table.querySelector('')

Below tableSub I want to select <br>, but I want to replace it with randomColors of cats from a generator I have created.