Hi Jane,
At this point in time, forget about a schematic as Royal (now TCI-Dirt Devil) has no idea what an Anniversary Edition Model#89103 even is.
You'll do best on Vac Parts+, (Henry Co.) eReplacementParts.com, and other websites discussed here on this forum.
Right now besides belts, I'd advise you to purchase (Qty.2 as they're cheap) 670744 Nozzle Plugs, (Flap that covers belt access hole on front of nozzle) an extra 285270 Nozzle Guard (Bottom Cover below Brush Roller), and a couple belt lifters @ $1.50 each. If you should need motor/brush roller ball bearings, they're dirt-cheap on eBay. YES, Brush Roller Bearings are cheaply and easily replaceable.
Remember to ALWAYS UNPLUG the vacuum prior to inserting the belt lifter through the belt from the bag discharge outlet side of the machine. Check that you have the belt installed correctly by spinning the shaft extension (pulley) CLOCKWISE as viewed from the front of the vacuum with your fingers. If you installed the belt INCORRECTLY, it will flip off the shaft when rotated CLOCKWISE.
As far as the belt is concerned, Ben is right on the money with P/N: 1672260001. Instead of trying to install the belt over the motor shaft extension with a screwdriver, a few belt lifters (one as a spare) are a good cheap investment while ordering parts.
Spending money on a few spare parts is worthwhile now being they're still available, as Royal is no longer, Royal an American company in Ohio, especially if the vacuum is in relatively good condition likely giving you several years (if not decades) more service.
Hope this helps,
Mike