How do I update my phone I can not get or receive service

See this Apple article: If you see No Service or Searching on your iPhone or iPad

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

If you still don't have a 'service' after that, see -> iPhone 7 Repair Program for "No Service" Issues

iPhone 7 Repair Program for "No Service" Issues - Apple Support

Hi,

Connect to wifi and update it.

Check this for more info Update your iPhone, iPad, or iPod touch - Apple Support (IN)