If you have a Cat 1, 2, or 3 Suite with the Concierge Service, they can help you make your Spa Reservations. Otherwise, you'll need to make them at the listed time in the Navigator and in person, on the first afternoon.
For the dining assignments, you get those when you checkin, they'll be stamped on your KTTW Card. The location of the tables in the dining rooms change in each of the three restaurants. For example, table 22 might be near a window in one restaurant but closer to the center in another one and in a completely different location in the third one. You can ask for dining room changes on the first afternoon, with the time and location listed in the daily Navigator.
hope that helps