How do I unpair a watch from my phone. The watch is no longer active

Unpair Apple Watch and remove Activation Lock

1. Open the Apple Watch app on your iPhone.
2. Tap My Watch, then tap All Watches.
3. Tap  next to your watch, then tap Unpair Apple Watch.

Your Apple Watch is erased and removed from your iCloud account, and Activation Lock is removed. For more information, see the Apple Support article About Activation Lock on your Apple Watch.

Or;

To unpair and erase watch and remove Activation Lock

From a web browser,sign in to iCloud.com with your Apple ID.

Go to Find iPhone.

Click All Devices at the top of the screen.

Click your Apple Watch.

Click Erase [device]. Select Next until the device is erased.

Click Remove from Account.