How to Hide Planaday API Admin Menus

function plt_hide_planaday_api_menus() {
	//Hide "Planaday".
	remove_menu_page('planaday-api');
	//Hide "Planaday → Welkom".
	remove_submenu_page('planaday-api', 'planaday-api');
	//Hide "Planaday → Instellingen".
	remove_submenu_page('planaday-api', 'planaday-api-general');
	//Hide "Planaday → CSS".
	remove_submenu_page('planaday-api', 'planaday-api-css');
}

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

Where do I put this code?