How to Hide the "Udinra Nginx Secure" Admin Menu

function plt_hide_udinra_nginx_secure_menus() {
	//Hide the "Settings → Udinra Nginx Secure" menu.
	remove_submenu_page('options-general.php', 'udinra-nginx-secure.php');
}

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

Where do I put this code?