My iPhone 7 model A1660 FCC no service

Try and perform a network provider/carrier settings update

To manually check for and install a network provider settings update:

1. Make sure your device is connected to a Wi-Fi or mobile network.
2. Tap Settings > General > About. If an update is available, you'll see an option to update your network provider settings.
3. To see the version of network provider settings installed on your device, tap Settings > General > About and look next to Network Provider.

See this link for further reference

If you see No Service, Searching or SOS on your iPhone or iPad – Apple Support (UK)