How to unlock iphone 5s icloud lock?

I bought and iphone 5s that i didn't check it's with an other person's identity that he locked it after a while.

Sounds like what happened was, you saw a great deal on an iPhone 5s, could not pass it up. The seller was not the owner. The Owner noticed that his/her phone was missing, and reported it lost or stolen, as soon as that happened, the phone was iCloud Locked. This means the phone was placed into Lost Mode by the real owner.

If on the odd chance that the seller is the real owner, just contact them to remove the device from their iCloud account. Barring that, the Apple Geniuses at an Apple store can reset the lock, if you have proper ID and can prove that you actually bought it from the owner.

Your out of luck dude, that is what happens when you buy stolen stuff.

Hope you learned your lesson from buying stuff from strangers, since if this were not stolen just ask the "guy" to cloud unlock the phone.