How to change Apple ID on Apple Watch 2
How do you change your Apple ID on Apple Watch 2 during setup?
Apple Watch Series 2
Hi
Apple Watch will be set up with the Apple ID that your iPhone is signed in to.
To use a different Apple ID on your watch, you would first need to change it on your iPhone and then pair the watch.
Sign in with a different Apple ID on your iPhone, iPad, or iPod touch - Apple Support