The latest update of Appdev includes a child theme that can be used for this purpose. All you have to do is to override the function mo_display_app_button_or_socials() in your child theme’s functions.php. As long as you have a method with the same name, WP will load the child theme’s function and ignore the one which is defined in the parent since there are checks in the parent theme for already defined functions.
You will not see any changes I make to this function in future updates, but if you are customizing, you don’t need those changes anyway.