i buy iphone 6s to someone but the problem the phone is locked , he told me was unlock , can you help me to unlock it ,,thanks

Then they didn't tell you the truth about it being unlocked.

You now have a few choices:

1. If they are the original owner have them follow this support article to "unlock" the phone for you.
2. If they are not the owner, they don't know who the owner is, or willing to help you with this, try to get your money back.

Again, there is no other way to contact them.