Keep your Apple Watch and iPhone close together
Open the Watch app on your iPhone
Tap My Watch
Tap General
Tap Reset
Tap Erase Apple Watch Content and Settings
Enter your passcode if prompted
If you have a cellular plan, choose to keep or remove it
Enter your Apple ID password if prompted to disable Activation Lock
Confirm the erase
Wait for the Apple Watch to reset and restart
Set up the Apple Watch again or leave it erased