How to reset your Apple Watch if you forgot your passcode
- Put your watch on its charger and keep it there until you complete these steps.
- Press and hold the side button until you see the power button in the upper-right corner of the display.
- Press and hold the Digital Crown until you see Erase all content and settings.
- Tap Reset, then tap Reset again to confirm.
- Wait for the process to finish, then set up your Apple Watch again. When asked, restore from a backup.
And then,
Remove Activation Lock on the device
Follow the onscreen steps to enter the Apple ID and password you used to set up your device or your device passcode. If you don't remember your Apple ID, try to sign in with an email address or phone number that you regularly use for Apple services.