Apple Watch 3 with iPhone 6 pairing problem

I have an iPhone 6. Apple just repaired my Apple Watch 3, but when it was returned to me, it was updated with iOS 7, and when I try to pair it I get a message that my iPhone iOS is out of date and to update it, but it is up to date with iOS 12.5.2. Is there anything I can do to get them working together again?