There are two main steps to reset your Apple Watch. First, you need to unpair your watch with your iPhone before you can reset it to factory settings. If you no longer have your iPhone or cannot unpair, this is not a problem. You can just jump straight to resetting your watch.
Unpairing Apple Watch with iPhone
To unpair your watch with your iPhone, you will need to keep the two devices close together. Open the Apple Watch app on your iPhone, go to the My Watch tab and tap on your watch.
Once you have selected it, tap the “i” next to the watch that you want to unpair and look for the “Unpair Apple Watch” option. Selecting this will bring up a window asking you to confirm. Your password may be required to continue.
Note: By unpairing your Apple Watch, your iPhone will create a new backup to restore later in you need to.
Resetting your Apple Watch
If you want to completely reset your Apple Watch to factory setting, you can do this without having your iPhone close by.
To begin, open the Settings app on your Apple Watch and select General > Reset > Erase All Content and Settings.
Select Erase All to confirm the reset and your Apple Watch will be reset to factory settings.
Once you have completed your reset, you can either set up your Apple Watch again or hand it over to someone else to set up with their iPhone. If you followed the Unpairing steps, you should have a backup of the Apple Watch, which you can either use to restore the same one or restore all your data onto a new one.