How to contact owner of AirPods I've found?

Hold the case close to the top-rear of your phone.

That should then prompt you to launch a url (to Apple’s FindMy servers)

IF the owner has placed the AirPods in “Lost Mode” and added a message as a recovery aid, it will show up there.

This might not work on “earlier” AirPods.

It’s unfortunate that the owner didn’t take the opportunity to add a “Recovery Aid” message when placing them in lost mode. 🤷🏼

The “next best” thing to do now is to return them to the most logical Lost & Found based on where you found them.

If they were found in a public area, that might actually be to the local law enforcement entity.