I don't think there is one on the member site. It's on the WDW site. I couldn't get it to accept my ressie #, but I've heard if you choose the restaurant, and then book it will ask if you have a # and works that way.
You can't make on line ADR's on the member site you have to go to the WDW website and go to book then dining reservations. In fact here is the link to make it easier.