Apple Watch unlock

The Activation Lock must be released by the original owner who set the lock. Details are in What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else - Apple Support and About Activation Lock on your Apple Watch - Apple Support

Without the original owner giving you the passcode , you cannot unlock the Watch.

You need to find the original owner and get the password there. If not, then you cannot unlock the watch.