I bought this watch used and have no idea who the previous owner was and there’s an activation lock. Help please?

The bad news is that unless you can contact the previous owner there's nothing you can do,no one on here or anybody at apple can help you.If you manage to track the previous owner then this is what they need to do;

What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else – Apple Support

There's no way around Activation lock, it's an anti-theft device. The phone is useless to you, turn it over to the police.