PHP form reset button - clear session with method="get" - php

Question

I have created a multipage form that is storing the data in sessions. Instead of using method="post" I am using method="get" to allow the user to click the back button and hold the data on previous pages to edit. I also have email validation happening in the PHP script.
How would I be able to have a submit button advance to the next page in the form and a Reset button to clear the session and stay on this page (or reload the page) without the session data appearing within the form fields?
I have tried modifying someone else's suggestion using the following without success. Here is the PHP script at the start of the document:
<?php
session_start();
foreach ( $_GET as $key=>$value ) {
if ( $key!="submit" ) {
$value = htmlentities(stripslashes(strip_tags($value)));
$_SESSION[$key] = $value;
}
}
$firstname = $_SESSION['Firstname'];
$lastname = $_SESSION['Lastname'];
$email = $_SESSION['Email'];
if(isset($_GET['clear'])) {
session_destroy(); // Or other session-unsetting logic
header("Location: form.php"); // Reload your page
}
else if(isset($_GET['submit'])) {
//next page logic
header("Location: form-2.php"); // Reload your page
}
?>
Here is the form within the page body:
<form class="mod-columns-form" method="get" name="mailform" action="form-2.php" onsubmit="return validateForm();">
<fieldset>
<label for="Firstname">First Name <span class="mod-error">*</span></label>
<input type="text" name="Firstname" id="Firstname" placeholder="first name" value="<? echo $firstname; ?>" />
<label for="Lastname">Last Name <span class="mod-error">*</span></label>
<input type="text" name="Lastname" id="Lastname" placeholder="last name" value="<? echo $lastname; ?>" />
<label for="Email">Email <span class="mod-error">*</span></label>
<input type="text" name="Email" id="Email" placeholder="yourname#domain.com" value="<? echo $email; ?>" />
<button name="submit" type="submit" value="submit" class="submit">Next</button>
<button name="clear" type="submit" value="clear">Clear</button>
</fieldset>
</form>

Answer 1

to free you from the data in the form , you can create a button , which perform reset the variables.
<button name="reset" value="resert">RESET</button>
you need to check the session this page, creating a small code block in php .
<?php
session_start();
if (!isset($_SESSION['Firstname']) && $_SESSION['Lastname'] && $_SESSION['Email'])
{
print "error";
}
?>