My new Apple Watch has activation lock from a different owner

You're yet another of the many who have come here just today who made a bad buying decision and you've very likely been scammed. Activation Lock as Limnos posted cannot be removed by you. Apple will NOT remove the lock on the watch. We cannot help you remove the lock on the watch. The ONLY person who can remove it is the person who put the lock on the watch. And I can pretty much guarantee you that is not the person you bought the watch from. The ONLY way Apple would help you is with the original purchase receipt, with the watch serial number on it. I'm sure you don't have that and you have no way to get it either.

Since you can't reach them, you need to accept you've wasted your money and the watch is totally useless to you. Facebook Marketplace is one of the absolute worst places one can buy an Apple device. If you can't get your money back, the only thing you can do with the watch is recycle it responsibly and chalk this up to a bad buying choice.

Read this --> The All Too Common SAD Reality of Buying … - Apple Community

Either the person didn't fully remove it from their Apple ID before they sold it, or they weren't the actual owner of the watch and don't have the information to remove it from their Apple ID.

Usually, if the person legitimately forgot to remove it from their Apple ID you can get them to remove it from their account. If they refuse to answer you after you have purchased it was most likely a scam and unfortunately, you have purchased an expensive paperweight.

The point of this Activation Lock is to deter thieves from stealing the devices as they will be useless to them. It is doing what it is designed to do and there is no way around it other than getting the original owner that had it signed into their Apple ID to remove it from their account. Once it is removed from their account then you will be able to sign it into your account and be assured that as long as it is attached to your Apple ID at that point it will not be useable to anyone else until you remove it. If you can't get in touch with the original owner and have them remove it, then it is going to be useless.

This support article has information about Activation Lock on your Apple Watch and how to turn it off as part of preparing a Watch for service or a new owner. --> About Activation Lock on your Apple Watch - Apple Support

- Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. Do this online at: Activation Lock support request - https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not state what currently constitutes proof. Prior to this new online service Apple typically required the original receipt issued by an Apple Authorized dealer and documented provenance (so typically it would be the original owner who does this, or a descendant with legal proof of ownership). Apple recommends you keep your receipt after you buy an Apple device. --> Keep your receipt after you buy an Apple device - Apple Support