How do I fix my iPhone when it says no service?

See if this helps: If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support

You can read Apple's support document about this........If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support.........but the bottom line is that you will need to get in contact with your carrier to have them troubleshoot your service and connection.

Since your phone has No Service, you will need to use another phone to contact your carrier.