Put your Apple Watch on its charger
Press and hold the side button until the power menu appears
Press and hold the Digital Crown until the Erase all content and settings option appears
Tap Erase all content and settings
Confirm the erase
Wait for the Apple Watch to reset
Set up the Apple Watch again
Restore from a backup if prompted
If you forgot the passcode and cannot access the watch, erase it using the Watch app on your iPhone
Open the Watch app on your iPhone
Go to My Watch
Tap General
Tap Reset
Tap Erase Apple Watch Content and Settings
Confirm the reset
If needed, use iCloud or Find My to erase the Apple Watch remotely
After reset, pair the Apple Watch again and create a new passcode