How to update iOS iPhone to 15.1
How can I update my iOS version
iPhone 7
Question marked as
You won't be able to upgrade to iOS 15.1 on that iPhone 7. All that will be offered is 15.7.9. It is not compatible with iOS 16 upgrade.
Connect the phone to a power source and a Wi-Fi SSID (not Cellular) and select Settings : General : Software Update. That should provide you with 15.7.9 for installation.