Apple Watch connected to iPhone but not working

Try and unpair it without your iPhone

1. On your Apple Watch, tap Settings > General > Reset > Erase All Content and Settings.
2. Type your password if prompted.
3. For GPS + Cellular models, choose to keep or remove your cellular plan.

• • If you want to pair your Apple Watch and iPhone again, keep your plan. 
  • If you don't want to pair your Apple Watch and iPhone again, remove your plan. If you aren't going to pair with a different watch or iPhone, you might need to contact your carrier to cancel your cellular subscription. 

1. Tap Erase All to confirm. This resets your Apple Watch to the factory settings.

Now you can set up your Apple Watch again. You'll need the Apple Account and password associated with the watch turn off Activation Lock.

Which Apple Watch are you trying to pair? Can you still access the watch?

If yes, try to erase it, as explained in this article:

Unpair and erase your Apple Watch - Apple Support

Or try these steps:

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1. Put your watch on its charger and keep it there until you complete these steps.
2. Press and hold the side button until you see the power button in the upper-right corner of the display.
3. Press and hold the Digital Crown until you see Erase all content and settings.
4. Tap Reset, then tap Reset again to confirm.
5. Wait for the process to finish, then set up your Apple Watch again. When asked, restore from a backup.

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copied from: If you forgot your Apple Watch passcode - Apple Support