Unable to restore Apple Watch to previous WatchOS 8 to be able to pair with iPhone 7.

I have a iPhone 7 (iOS 15.7) and paired with Watch SE (WatchOS 8).

My husband unpaired the watch, paired it with his iPhone 13 (iOS16) and then updated it to watchOS9.

Now I am unable to pair my watch back to my iPhone 7 (iOS 15.7) because iOS 16 is not supported in iPhone 7.

Now I am in trouble !!

I have tried factory reset on the watch but it did not reset back to watchOS 8. The factory reset only delete all apps and data.

Is there a way to restore my phone back to previous watchOS so I can pair my watch to my iPhone 7 ?