To reset the watch to factory settings:

1. Open the Withings App.
2. Tap your Devices in the upper right.
3. Find your device and scroll down to the very bottom.
4. Tap Dissociate this product and then Remove from my account.
   Note: If you don't see the device in your devices section, simply skip to step 5.
5. Press and hold the button on the side of the watch for 10 seconds. Workout mode will start after pressing the button for about one second, but continue holding the button until the watch vibrates twice.
6. After the watch vibrates twice, release the button and the activity hand will move to the 50% marker.
7. Press the watch button 5 times. Each time the button is pressed, the activity hand will get closer to the 0% marker. Allow the hand to move to the next marker before pressing the button again.
8. After the activity hand has reached the 0% marker, the watch will vibrate and the hands will show 10:10.
9. The watch is now ready to be configured.

You will find instructions on how to configure your watch here.