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 asked
Wait for the unpairing process to finish
If you do not have the paired iPhone, on the Apple Watch open Settings
Tap General
Tap Transfer or Reset Apple Watch
Tap Erase All Content and Settings
Enter your passcode if prompted
If asked, choose to erase the cellular plan
Confirm the erase
Wait for the Apple Watch to restart and complete the wipe