on my 23SS, you look under the sofa and there's a gold-colored motor, i think, at the very back. it has a small shaft coming out with a pin thru it. the socket on the end of the crank, fits over it and that turns the motor manually.
not sure if it's in the same area in the 21SS. it takes a lot of cranking to get it in.
there's no hole or access hatch to do this, on my 23SS.
it also, might be under the dinette, somewhere. it should be on the floor of the slide, somewhere.
you also might look at some of the other posts in the Roo or Shamrock sections for other 21SS owners. send them a PM.
who did you buy from? the dealer should be able to help. if not, call RVWholesalers and see if someone there can help you.