You can use a large C-Clamp to compress the caliper piston.
AnswerThere is not enough information in your question. A cylinder piston you do not compress, you compress the rings in the piston. There are pistons in the brake system. There is no way of knowing the problem without being more specific.I'm assuming you mean the caliper piston. If it can't be compressed, replace the caliper.
C or G clamps.
turn it in clockwise with a pair of needlenose
You will need a caliper rewinding tool
Similar to any other caliper piston, you might used a C-Clamp that has been covered in some protective coating to prevent it scratching the caliper. Ideally the C-Clamp would not directly compress the piston edge but some piece of flat metal, laid out in a way that would allow it to spread the force across the piston's diameter.
It requires a special tool to turn and compress the piston in at the same time.
If it is the front brake use a "C" clamp to retract piston If it is the rear and the parking brake is used by this caliper piston is threaded and a special tool (not expensive) available at Sears or auto parts to "screw" piston into caliper body
If the emergency brake is not connected to the caliper use a "c" Clamp If the emergency brake is connected to that caliper a special tool (not expensive available at Sears or auto parts) is needed Caliper is threaded. Turn Clockwise to compress
If the emergency brake is not connected to the caliper use a "c" Clamp If the emergency brake is connected to that caliper a special tool (not expensive available at Sears or auto parts) is needed Caliper is threaded. Turn Clockwise to compress
Shade tree mechanics use a C-clamp and a flat steel bar to compress the piston. I have also used a large adjustable Channel-Lok-type pliers to compress.
with a large pear of channel locks,or a caliper compressor