How would a perpetual motion machine reverse entropy in a (closed system)?

i know its not possible cause of the law of thermodynamics but, what if a perpetual motion machine is built, how would it reverse entropy in a (closed system)? how would it gather enough information to do so? what does it have to do exactly? please take sci-fi out of the mind and just think about it. please provide good info and please no negative comments. thank you.