If you are working with a HAL rep (PCC) or TA, contact them directly and they will make the arrangements. If you booked direct online, try contacting Ship Services, although they may not be able to do anything until closer to the sailing date. Last resort is to go directly to the main dining room or reservations desk, when you board, and make the arrangements through them.
HAL_Ship_Services@hollandamerica.com
800.541.1576