How to reset my Apple Watch

Perhaps one of these articles will help:

Unpair and erase your Apple Watch - Apple Support

If your Apple Watch isn't connected or paired with your iPhone - Apple Support

Set up your Apple Watch - Apple Support

Or this;

To unpair and erase watch and remove Activation Lock

From a web browser,sign in to iCloud.com with your Apple ID.

Go to Find iPhone.

Click All Devices at the top of the screen.

Click your Apple Watch.

Click Erase [device]. Select Next until the device is erased.

Click Remove from Account.