Reset Apple Watch settings. On Apple Watch, open the Settings app , go to General > Reset, then tap Erase All Content and Settings. Or, open the Apple Watch app on iPhone, tap My Watch, go to General > Reset, then tap Erase Apple Watch Content and Settings.

If you can’t access the Settings app on Apple Watch because you’ve forgotten your passcode, put Apple Watch on its charger, then press and hold the side button until you see Power Off. Firmly press the Power Off slider, then lift your finger. Tap Erase all content and settings.

After the reset finishes and Apple Watch restarts, you need to pair Apple Watch with iPhone again—open the Apple Watch app on iPhone, then follow the instructions shown on iPhone and Apple Watch.