You can reset the watch by going into settings (the gear icon) on your watch and scroll down to the bottom. You can access the Settings menu by swiping right and scrolling down until you see the gear icon OR you can swipe up to the quick menu and press the gear icon there. There you will see the reset option. It will inform you that your data on the watch will be erased. Once you tap reset again after this, the watch will fully reset.