In order to hard reset a Apple Watch 42mm, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Apple Watch 42mm device will be brought back to the default configuration of a brand new device.
1. Press'n'hold the Side button until Watch options appear.
2. Tap tand hold Power Off option for five seconds.
3. Lastly, tap Erase all content and settings.
4. Done.