Activation lock bypass

You don’t

the activation lock is not really on the watch it's a theft protection measure on apples servers

it needs to be removed

https://support.apple.com/en-us/HT205009

if you don't know your appleID 

Recover Your Apple ID - Apple

if that does not help you then you need the assistance of apple 

Additional Support - Activation Lock (apple.com) and or

Get Support (apple.com) , Genius Bar Reservation and Apple Support Options - Apple

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

You don't.

That's the entire point of it. It is intended to render a lost or stolen device useless to anyone other than the rightful owner. It does that by requiring the credentials of the iCloud account that is signed into the phone to activate FindMy.