if you the person. then you should try to return it to him. and if you do not know the person then try to find him through this topic. and if even then you did not find the person then give the amount to a poor needy person.
It's very hard task to find who is the real owner of that btc that he received because bitcoin is known for being anonymous so it will be hard to track down the real owner because many members in this forum will act like the real owner.
Giving that accidentally received btc to a poor person is not a good idea because just like finding real owner, many members also will beg for that and manipulate that they are very poor and really need bitcoin but the real thing is they have many bitcoin and they want some more.
So it's better if he keep and save that accident btc that he received so someday he will earn great amount of money.