How can I get WatchOS9 with iOS 15?

Hi,

my grandpa has a problem with his Apple Watch.

He has a series 7 Apple Watch and an iPhone 7.

He wants to get his WatchOS 9 but can’t without updating his phone to iOS 16 which iPhone 7 doesn’t support. Is there another way to get WatchOS 9 without changing his phone?

BTW when I go into Updates it just shows “an error occurred whilst searching for an update” or something like that (I’m polish so I can’t quote exactly in English lol)

im guessing it’s because his phone isn’t updated but it might be important.

thanks for any responses

love <3