How to Hide the "Yandex Mail SMTP" Admin Menu

function plt_hide_smtp_yandex_mail_server_menus() {
	//Hide the "Settings → Yandex Mail SMTP" menu.
	remove_submenu_page('options-general.php', 'yandex-smtp');
}

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

Where do I put this code?