Server error 500 after installing wp File Manager plugin

Hi ive got a server error 500 on my site. I downloaded wp File Manager plugin cause i didnt have acces to ftp. I wanted to add this line of code:

add_filter(‘widget_text’, ‘do_shortcode’);

Because i wanted to work with the Contact Form 7 Widget. So i downloaded the functions.php file and added the line into a function, which probably caused the error. Now without having acces to the ftp how do i acces my site and load the old functions.php back?