1991 Camry: How can I manually close my sunroof

Now this is from a later model but should still be valid for yours as well. from here Remove the front sunglass holder and pull down the front of the headliner then you can access the sunroof motor, if the cable has only separated and not completely jammed itself in the housing then you should be able to remove the sunroof motor and manually pull on the glass forward to position the glass back closed, you can not however position the glass up/down manually because the cables are directly connected to the lift arms and require motor drive to position up/down.

Now that is for the sunroof I think this is the one for the moonroof. To close the moonroof

1. Grasp the cover to the rear cooling system, located to the rear of the moon-roof control. Remove the cover by pulling it down. Set the cover aside.
2. Locate the two moon-roof-control-cover retaining screws beneath the cover. Insert a Phillips-head screwdriver into one of the screws. Turn the screwdriver counterclockwise until the screw is completely loose. Repeat the process on the other screw. Set the screws aside. Remove the moon-roof control cover and set it aside.
3. Remove the tool bag from beneath the front passenger's seat. Remove the crank-shaped screwdriver from the tool bag. Insert the screwdriver into the drive-shaft screw, located beneath the moon-roof control cover. Turn the screwdriver counterclockwise until the screw is completely loose. Remove the screw and accompanying spacers. Set the screw and spacers aside.
4. Pull the moon roof forward by hand, as far as it will go. Insert the screwdriver into the drive shaft. Turn the drive shaft clockwise with the screwdriver until the moon roof is completely closed.

Ultimately of course, you will have to get it fixed. It does sound like either your motor or the gear sub assembly will need to be replaced. This Forumhas some great info. Not very pretty images but they do give you an idea. Good Luck