If you forgot the Apple Watch passcode, you cannot unlock it without erasing the watch
Put the Apple Watch on its charger and keep it there
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
After the watch resets, pair it again with your iPhone
Restore from a backup if available
If Activation Lock appears, sign in with the Apple ID used on the watch
If you need help, use the Apple Watch app on iPhone or contact Apple Support