: Plug in your modem and open the Huawei Modem Code Writer (running as Administrator is often recommended). Select Device : Choose the detected modem from the list.

Run as Administrator.

The phone must be powered off and connected via USB while holding a specific key combination (varies by model) to enter Download Mode (often shown as a black screen with no display).

Your 4G modem works, but it refuses to connect to a specific LTE band (e.g., Band 20 @ 800MHz) that provides better coverage in your area. A Code Writer can modify the bandmask settings.