There are irons and ironing boards for guest usage on most ships. It's best to wait until the second day to try to use them and then do all your clothes at once.
You can use those travel steamers.
You can hang the clothes in the bathroom and turn the shower on full hot and let them steam on the hanger. The wrinkles will fall out fairly soon.
There are services on board for a fee too.
Regards,
Thomas