How can I solve my no service problem

Select this link 'If you can‘t make or receive calls on your iPhone' --> https://support.apple.com/HT204027

- "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 or Searching on your iPhone or iPad' click here --> https://support.apple.com/HT201415