The fork is supposed to spring back on its own. Otherwise, you'd have to dismount and pull it back after every bump.

In normal use, your weight would partly compress the fork, leaving most of the travel for bumps, but also having room to prevent topping out on the rebound.

From your description, I wonder if dried oil has become sticky, of perhaps the seals are adding friction.

Short of taking apart, you might try oiling and working it back and forth to see if it frees up.