How to update software on iPhone 7

The Related Article is about iOS 16.7.6. You can't update an iPhone 7 to that. For the iPhone 7, the latest release of iOS 15 (currently iOS 15.8.1) is the end of the line.

If you are not yet up-to-date with respect to iOS 15, see:

Update your iPhone or iPad - Apple Support

Updating iOS: common issues and solutions - Apple Community