What if you have a pc

The fact you don’t have a Mac is irrelevant; anything that needs to be done can be done with iTunes on a Windows 7 or later PC.

Here are the general instructions—>If you see No Service or Searching on your iPhone or iPad - Apple Support

As you have an iPhone 7 this might apply to your situation—>iPhone 7 Repair Program for "No Service" Issues - Apple Support

See if this helps: https://support.apple.com/en-us/HT201415. Are you sure it is not a carrier issue?