Use SIM Toolkit
This page is for devices with calls and mobile data.
Open SIM Toolkit > tap an item in the SIM card's menu.
The SIM Toolkit app shows the services your wireless service provider puts on your SIM card, such as your balance, top-up, and operator services. Features vary by wireless service provider.
If there is no menu, the app says so. This happens when no SIM card is inserted, the SIM card is locked, or it has no such services.
Checked against the LuneOS code and installed apps. Nobody has tried these steps by hand yet, so tell us if something differs.