Update watch to iOS 9
I have a Series 4 watch and an iPhone 6s. I am trying to update my watch to iOS 9 and get the message that I need to update my phone OS first. I am currently up-to-date on the phone OS (15.7) so I don't understand what steps I should take next to get iOS 9. I unpaired and then re-paired the watch hoping that would clear things up but am still stuck. Suggestions please!
iPhone 6s, iOS 15