Pairing series five Apple Watch with a new iPhone 7 that only can update to 15.8.2 because it’s an air talk phone
It is paired with a different iPhone 7.
iPhone SE, iOS 17
In case the Apple Watch has already watchOS 10 installed, you can only pair it to an iPhone that has iOS 17 installed.
You can unpair the watch from the other iPhone 7, without the iPhone nearby. Have a look at the steps mentioned in this article:
If you can't pair an Apple Watch with your iPhone - Apple Support