Adding admin top-level menus

Question

You can change the first Submenu text with the following script:

function __test_menu() {
    global $submenu;
    //var_dump($submenu); //check yourself
    $submenu['unc_gallery_admin_menu'][0][0] = __( 'Test', 'textdomain' );
}
add_action( 'admin_menu', '__test_menu' );

Please note, your plugin is error-prone, throwing warning messages. Always develop things with WP_DEBUG to true. And don’t write hardcore texts, better write them in gettext functions. i.e. write __( 'Test', 'textdomain' ); instead of 'Test';. It will make your plugin translation-ready. Good luck.