Break Help

[300EXrider356]

Well the story goes, I was changing my rear break pads and my brother came into the garage, and decided to sit on my quad, i was like ok. Then he started pushing on the break pedal repetedly, pushing the piston out. But it wont go back in, i cant figure it out, any help?
Thanks

[pimpin330ex]

what did u try doing my neighbor did the same thing and i just used a flathead screwdriver and pryed it open and it worked fine.