There isn’t a specific dining reservation desk, but the DR does have desks on both sides of the door to the MDR’s.
If you can’t catch the DRO/Maitre’d on lunch day, ask for what you want at the first dinner.
All the last cruises we’ve been on, he was not at the lunch MDR, but was at the Dinner. Extremely busy, so we told our waiter and head waiter. They conveyed for us. We were able to get TD on ALL our restart cruises. 8 cruises.
I would not worry about 1 night. If you get the same time, same table every night, you’ll already be in the computer for it.