Days after getting a refund and reshipment of items that never arrived, a deaf neighbor dropped off my original package since it was misdirected to her apartment instead of mine. What should I do with the original package now?

Days after one of the items got refunded and the other got reshipped due to never arriving at my door, my deaf neighbor on the other side of the apartment complex dropped off my original package that I reported as missing.

Can I open the package? Do I need to return it? What should / can I do with it? Or do I just keep it and not notify Amazon? And therefore retroactively have a free product and another one that's now a 2-for-1 deal?

What's the standard procedure for what to do when a package finally turns up albeit late and after I had already completed a missing package claim? Thanks in advance.