Try erasing the watch by:
The steps below can help show you how to reset your Apple Watch:
If you forgot your Apple Watch passcode - Apple Support
- Put your watch on its charger and keep it there until you complete these steps.
- Press and hold the side button until you see Power Off.
- Press and hold the Digital Crown until you see Erase all content and settings.
- Tap Reset, then tap Reset again to confirm.
Wait for the process to finish, then set up your Apple Watch again.
Note when you setup again it will likely say the the Activation Lock is on and you will have to get it turned off. To turn it off see:
https://al-support.apple.com/#/getsupport