advise about iphone 8 plus

some one who is coming from USA sold me this iphone 8 plus, battery was 0% so i couldn't check it before his arrival, after charging and when checking it. i found it locked with apple id, i don't know this apple id info, also i cannot find the buyer any more. what can i do, i left it open for long time, but it is not stolen, might be the original owner forget to remove his apple id from this device.