1990 Chevrolet Corvette - parking brake question

How can I get a 1990 Corvette that uses the rear calipers as parking brakes to hold the car from moving?

Have the parking brakes adjusted I guess . Other than that Not sure what the problem you have is .

If they don’t hold the car, then they are broken, out of adjustment or the brake pads and rotors on the rear are too damaged to acheive that.