you need to use needle nose pliers and twist and push inward at the same time. rear caliper retract tools are easier though. you can either buy one, or rent it free(you get your money back when you return it) from autozone or what not.
I've seen rear calipers damaged using needle nose pliers to reset the piston. D.Passat00, hit the nail on the head with renting a Caliper Piston Retraction Tool from a local Autoparts store. You can also buy one from Adirondak Auto Parts for about $48.00!
So much easier with the proper tools, I strugled on for an hour with round nosed pliers, c clamps,bits of wood & sore hands with no joy , went to garage & purchased the piston retractor tool.......15 min later both brakes done. :lol: