If the wheels are already bolted on, first try flexing the rear cables to see if they're just sluggish. The brake shoe return spring pressure will pull the cables back. If that doesn't work, you'll have to pull the drums off and use a pry bar to push the parking brake lever into the rear shoe to pull the cable back. Once that is done, both rear shoes must be touching the large anchor pin on top of the backing plate, and you must be able to use your thumb to push the parking brake strut bar forward a good 1/8" against the anti-rattle spring pressure. If you don't observe both of those, the cable is not fully released.