Keep your Apple Watch and iPhone close together
Open the Watch app on your iPhone
Tap My Watch
Tap All Watches
Tap the info button next to your Apple Watch
Tap Unpair Apple Watch
Enter your Apple ID password if prompted
Confirm the unpairing
If you do not have the paired iPhone, on the Apple Watch open Settings
Tap General
Tap Reset
Tap Erase All Content and Settings
Enter your passcode if prompted
If asked, choose to keep or remove your cellular plan
Confirm Erase All
Wait for the Apple Watch to finish wiping and restart