White Screen of Death After Editing .php File

Hi,

I am in desperate need of help. I was using a staging plugin to edit a clone of an existing website.

In the process of trying to make some changes to the Header and Logo, I put in this code into the functions.php editor:

add_action(‘wp_footer’, ‘ava_mobile_header’, 5);
function ava_mobile_header(){
?>
<script>
(function($){
$(window).scroll(function() {
if($(window).width() <= 989){
var header = $(‘.html_header_top.html_header_sticky #header’);
header.addClass(‘header-scrolled’);
}
});
})(jQuery);
</script>
<?php
}

It didn’t do what I was hoping for so I deleted it only leaving:
?php

In the functions.php editor. This is when the white screen of death occurred.

How can I solve this issue? Since the staging site does not have a separate link from the live site, is it even possible to fix this problem through an FTP server? Are there any other ways? Any help would be appreciated!

Thanks in advance.