How to clear activation lock on iPhone watch

First, try this:

If you forgot your Apple ID password - Apple Support

Activation Lock is designed to prevent anyone else from using an Apple Watch if it's ever lost or stolen.

About Activation Lock on your Apple Watch - Apple Support

Activation Lock is an anti-theft feature that cannot be bypassed. Only the previous owner can remove the lock by using their Apple ID & password. Apple will not help you find the previous owner. If the previous owner cannot or will not remove the lock, then the watch is useless to you or anyone else. Try to get a refund (through eBay) or dispose of the watch properly. In the future, see the 'Before you buy a watch from a third-party' section in:

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

If you are the ORIGINAL owner, then see the 'Start a support request' section in:

How to remove Activation Lock - Apple Support

See If you forgot your Apple ID

or

If you forgot your Apple ID password

or

If you forgot your Apple Watch passcode

or

How to remove Activation Lock

also

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