for the details. Just see the maitre'd at the desk in the main dining room entrance. I'd go there in the morning and order it for that evening. You can also see your waiter, but if you want it to be a surprise it may be hard to order it with your waiter if your friend is nearby.
It is typical to be asked if a special occasion will be happening during the cruise when you make the booking. Did you say your friend was having a birthday?