Trying to factory reset iWatch

Trying to reset my iWatch, and I've forgotten the passcode, I saw you can hold it to the charger and then hold down the side button to bring up the power off bar. When you hold that down, it will ask you if you want to reset it. The issue is though, after I hold down the side bar and the power bar shows up, nothing happens after I try holding it out, it doesn't even register I'm holding it down