Found an IPhone
What do I do if I found someone’s iPhone but can’t get any information, to return it to its owner?
Question marked as
If the device is able to connect to the Internet, you can try holding down the home button (or right side button on models without a home button) to talk to Siri, and say "whose iPhone is this?"
If it is not online or if that does not work, I'd recommend turning it into local authorities.