Redirect Issue with back button

PHP Code:

---

<?php
    
    if(isset($_POST['submit']))
    {
        header("Refresh: 5; url=test.php");
        $success=1;
    }
    
?>

<?php
    if($success==1)
        echo "success";
    else
    {
        ?>
<form method="post" action="">
<input type="submit" name="submit" value="Submit">
</form>

<?php
}    
?>

---

I'm trying to post a success message on the same php page. When I press the back button on test.php it returns to the page with the success message again. How can I get back to the form when I press the back button instead and only display the success on submission of the form?