iPhone 7 has no service after update

Read this document if you can‘t make or receive calls on your iPhone --> If you can't make or receive calls on your iPhone - Apple Support

- "Find out what to do if you see "No service" or "Searching" in the status bar. You might not be able to make or receive calls on your iPhone if you have certain settings turned on, if your software isn't up to date, or if there's a problem with your network."

If you see No Service, Searching, or SOS on your iPhone or iPad read this document --> If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support

Have you tried the steps in this Apple article?

If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support