如何实现令牌过程以阻止用户在提交表单后返回

Hi i have a multi step form , so far so good it is validated with java and php , but what i need yet is to disable the user going back after submitting .

So this mean i want to stop or to erase the filled fields if the user click back from the redictet page after submitting my form i have read somthing about a hidden token input over but i dont know how to implement it for my needs .

So here is my proces.php this :

$emotion = $_POST['emotion']; 

if($emotion == 'Basic Pack') { 
session_start(); 
$_SESSION['form_finished'] = true; 
header('Location: /new/basicc.php'); 
} elseif($emotion == 'Deluxe Pack') { 
header('Location: html6.php'); 
} elseif($emotion == 'Premium Pack') { 
header('Location: html7.php'); 
}

in the destination page this case basicc.php this

<?php

session_start();
if(!$_SESSION['form_finished']) {
    header("HTTP/1.0 404 Not Found");
    exit;

}
?>

How can i stop my user to go back or direct him to a error or at least delete his filled fields if he chose to go back after submitting ?

any help would be welcomed . thanks in advance