Erasing Apple Watch
Do I need to erase my Apple Watch before I send it in for a trade in?
Apple Watch
What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else
https://support.apple.com/en-us/HT208855
M1 Mac mini, macOS 11.0.1; Watch, series 5 GPS/cellular, watchOS 7.1; iPad Pro 2nd Gen, iPadOS 14.2; iPad Air 2, iPadOS 14.2; iPhone 12 Pro, iOS 14.2.1; TV 4th Gen, tvOS 14.2 HomePods, audioOS 14.1 and Airport Express w/ Airplay 2