Hello and welcome to Just Answer!
There is a park brake cable tensioner under the drivers side of the vehicle along the outside of the frame near the fuel tank. You need to turn the nut clockwise so it tightens the the parking brake cables. You need a 13mm deep socket and a pair of vise grips to hold the bolt from turning when you tighten the nut.
If you run out of adjustment or your socket can't reach the nut, you can tighten the park brake star wheel adjusters. The star wheel adjusters are behind the backing plate at each wheel and there is a rubber plug in the backing plate above the axle. Jack the rear axle up so the rear tires are off the ground and remove the rubber plugs. Then rotate the star wheels with a flat blade screw driver or brake adjusting tool till you feel some drag while rotating the wheels. Once you feel the park brake drag, back off the star wheel about 1/2 to 1 turn. I can't remember which way you have to rotate the star wheels, so if the parking brakes don't tighten up, you could be turning it the wrong way.
I hope this helps, let me know!