How to fix my iphone no service

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

Also read this slightly different list of possible reasons and things to try if you see No Service, Searching, or SOS on your iPhone or iPad --> If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support