Firmware is typically installed via USB. It is highly sensitive; using the wrong resolution file can "brick" the board or result in an upside-down or distorted image.
Often requires checking the 1.8V and 3.3V rails. If voltages are present, the eMMC firmware is likely corrupted and needs a full dump rewrite.
This guide provides an overview and instructions related to the firmware string, which is commonly associated with the Jabil (Greenwave) GN01 router hardware, often used by internet service providers.