IF you like to insert a facebook like button then first of all you need to create a child theme. Create a functions.php file and then hook your scripts in wp_enqueue_scripts() functions. For more reference https://codex.wordpress.org/Function_Reference/wp_enqueue_script
I’m afraid I don’t have the skills to do that! Does Theme Horse provide one-off technical assistance for this sort of thing – i.e. can someone do it for me?!