How to download and install iOS 15.7.1 update on my iPhone 7?

Hello ~ Click on the links below for information that may be helpful…

Update your iPhone or iPad - Apple Support

If your iPhone or iPad won't update - Apple Support

As noted in the next link below iOS 15.7.9 is the current version and the highest version you can upgrade that particular model of iPhone.

About iOS 15 Updates - Apple Support

~Katana-San~

You can't download iOS 15.7.1, but you CAN download iOS 15.7.9.

Have you tried to update your iPhone and if so, what happens when you try?