What would you do if you managed to come across someone else's private key and it's worth an amount that most people would 'prefer not to lose', assuming you have no [idea who it belongs] to or [location clues]? Eg. Sweeping through common books' text for BIP39-based keys.
I suppose you could send a dollar's worth to a different address and hopefully they'd get the hint.
I will advice the person to take to the nearest police station or a radio or television station to announce. It. Or if there is no any other way for you took the owner and your mind to be pure as it is. You should come here and make a clear announcement so if the coins should be use for donation, people would still say it and tell what to do here.