I can't unpair my Apple Watch from my iPhone 12 can anyone help?

Remove  Watch from Apple ID -

Go to icloud.com and login

Open Find iPhone.

In the All Devices pulldown menu select your Watch.

In the resulting sheet that appears to the right choose erase Apple Watch.

Then Remove the watch from your Apple ID.

This should reset the watch to the factory settings for you to setup as new and repair to your iPhone.

You can restore the watch from a previous backup if you have one.

M1 Mac mini, macOS 11.1; Watch, series 5 GPS/cellular, watchOS 7.2; iPad Pro 2nd Gen, iPadOS 14.3; iPad Air 2, iPadOS 14.3; iPhone 12 Pro, iOS 14.3; TV 4th Gen, tvOS 14.3  HomePods, audioOS 14.3 and Airport Express w/ Airplay 2

Without any other info, perhaps these articles will help:

Set up your Apple Watch - Apple Support

How to pair your Apple Watch with a new iPhone - Apple Support

If your Apple Watch isn't connected or paired with your iPhone - Apple Support