The plugin does not work in my website

Hi

My website is https://www.ultimech.com/wordpress

The search experience with my theme is very poor so I wanted to install a plugin to improve that. I installed your plugin but the live search does not work. I am using the oldest version of the theme as it works better. However, in order to make the search box appears, I had to add the following code:

add_filter('wp_nav_menu_items','add_search_box', 10, 2);
function add_search_box($items, $args) {
ob_start();
get_search_form();
$searchform = ob_get_contents();
ob_end_clean();
if( $args->theme_location == 'Header' )
$items .= '' . $searchform . '';
return $items;
}

Is there anyway to make this plugin work onto my website?

Thanks
M

https://www.ads-software.com/plugins/daves-wordpress-live-search/