Lock Apple Watch

when you get in contact have him do the steps

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

Activation Lock prevents lost and stolen Watches from being used by other people. Only the original owner can unlock the watch. That watch is useless to you.

M1 Mac mini, macOS 12.1; Watch, series 5 GPS/cellular, watchOS 8.3; iPad Pro 2nd Gen, iPadOS 15.2; iPad Air 2, iPadOS 15.2; iPhone 12 Pro, iOS 15.2; TV 4th Gen, tvOS 15.2; HomePods, audioOS 15.2 and Airport Express w/ Airplay 2