I changed all 4 pads on my blazer. Now the rear brakes are locking up and not releasing the rotor...need help

To test.
Crack bleeder screw.
If brakes release the brake system is holding pressure on caliper.
Next step is to crack brake line in front of rubber flex hose.
Then if it holds pressure the rubber flex hose is bad.

When bleeder screw is opened and it is still holding the pads on
you caliper pistions /or sliding pins are binding/sticking.
MT