Bought iphone xr thur 3rd party its lock to user how do i get in contact with user

There is no way to get in contact with the user if the phone is activation locked, Apple’s theft deterrent feature. Most likely you bought a stolen iPhone, and you will never be able to use it. Return it for a refund.

Here is some sobering information→The All Too Common SAD Reality of Buying a Used iPad/iPhone

You don’t.

Return it and get your money back.

You can try contacting Facebook buyer protection.

You lose - big time. The seller wins getting funds they should never have received.