How do I add a PHP code that will always open/create a new text file and write user input once user clicks 'Submit' button

How do I add a PHP code that will always open/create a new text file and write user input once user clicks 'Submit' button.

This is the html code

<form action="save_redirect.php" id="#form" method="post" name="#form">
  <label>Email:</label><br>
  <input id="email" name="email" placeholder='Enter A Valid Email Address' type='text'>
  <br>
  <input id='btn' name="submit" type='submit' value='Submit'>
  <?php
  include "include/redirect.php";
  ?>
</form>

This is the php code I already wrote for redirecting.

<?php
if(isset($_POST['submit'])) {
  // Fetching variable of the form which travels in URL
  $email = $_POST['email'];
  $myfile = fopen("text.txt", "w");
  fwrite($myfile, $email);
  fclose($myfile);

  if($email !='') {
    header("Location:https://www.formget.com/app/");
  }
  else {
    ?><span><?php echo "Please fill the email field! This is where you'll receive script files on.";?></span> <?php
  }
}
?>