Before messing with the park-brake adjuster, adjust up the rear brake shoes with the star-wheel adjusters.
Then, go to that long threaded rod adjuster that is located about at the rear of the cab, driver-side, and adjust the park-brake, only if necessary after rear brake adjustment.
On my truck, it takes a 1/2" ratchet-wrench to adjust, and vise-grips to hold the rod still.