how to erase series 2 watch without pass

If passcode is the only problem then you can follow the steps in this article

If you forgot your Apple Watch passcode - Apple Support

If you come across an Apple ID and password request you don't know then you have a much bigger problem - come back.

Sorry, but without knowing the Apple ID password, the Apple Watch can't be erased, or the Activation Lock disabled:

Unpair and erase your Apple Watch - Apple Support

About Activation Lock on your Apple Watch - Apple Support