How does someone reverse power-of-attorney?

Question Details:

My father had to sign over power-of-attorney before going through surgery, now my brother is holding all his checks and bank cards and using his money at will. My father is totally capable of handling his finances and has no need for power of attorney. He signed this power oveer while in the hospital, what does he need to do to get this reversed and get his checks and bank cards returned to him? Important Notice