How to Hide the "ISL Pronto settings" Admin Menu

function plt_hide_chat_button_for_isl_pronto_menus() {
	//Hide the "Settings → ISL Pronto settings" menu.
	remove_submenu_page('options-general.php', 'dd-isl-pronto');
}

add_action('admin_menu', 'plt_hide_chat_button_for_isl_pronto_menus', 11);

Where do I put this code?