On my Rockwood 5th wheel it is located under the entrance door. Fold down the steps, get on your hands and knees and look under the door. *IF* like mine there should be a hole there to put the crank handle into.
Same handle manually raises/lowers the landing gear. That hole is inside the curb side LP tank compartment, behind the tank, taped over with black tape. They really tried to hide that one. And if you carry some 30 amp fuses and know where the landing gear inline fuse holder is, (near the battery) you won't need to crank it very often!