Can't get into site after code addition

I know next to nothing about programming but I can copy with the best of them. So, trying to add a search box to my navigation menu, I copied this code (from https://bavotasan.com/2011/adding-a-search-bar-to-the-nav-menu-in-wordpress/) into my functions.php (in my Pinnacle child theme):

add_filter( ‘wp_nav_menu_items’,’add_search_box’, 10, 2 );
function add_search_box( $items, $args ) {
$items .= ‘

• ‘ . get_search_form( false ) . ‘

‘;
return $items;
}

So now I can’t get into the site at all (it tells me to contact the server administrator), and I’m guessing it’s because it’s changed the menu structure, which I don’t know how to access from outside of WordPress (I’m using I-Page file manager).

https://www.ads-software.com/plugins/menu/