Don’t force restart your Apple Watch if you're updating watchOS. After you see the Apple logo and progress wheel on your Apple Watch, leave your Apple Watch alone and on its charger until the update finishes. You should force restart your device as

On your Apple Watch, tap Settings > General > Reset > Erase All Content and Settings. Type your password if prompted. For GPS + Cellular models, choose to keep or remove your cellular plan. If you want to pair your Apple Watch and iPhone again, k

Select your Apple Watch under My Devices. Click on the X next to your Apple Watch to remove it. Click Remove to confirm. Because your Apple watch has already been factory reset, there is no need to worry about the warning when selecting "Remove."