I have never done a Chammps restaurant. Many of the places that I shop which require a manager's name, the manager is supposed to be interacting with guests, and when they come to your table you get the name. If they don't, ask your server that you'd like to talk to a manager, and ask the manager about function rooms.
I have done it twice. I just flat out ask at the end for the manager's name, especially since there is likely to me more than one on duty. If there is only 1 on duty, you could call immediately after and ask for the manager.