How to Hide Notifier To Slack Admin Menus

function plt_hide_notifier_to_slack_menus() {
	//Hide the "Notifier" menu.
	remove_menu_page('wpnts_notifier');
	//Hide the "Notifier → Dashboard" menu.
	remove_submenu_page('wpnts_notifier', 'wpnts_notifier');
	//Hide the "Notifier → Settings" menu.
	remove_submenu_page('wpnts_notifier', 'wpnts_notifier_setting');
}

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

Where do I put this code?