Official firmware files usually come in .zip or .img format. Look for names like:
J4 header near PMIC: Pin 1 = GND, Pin 2 = TX (3.3V), Pin 3 = RX (3.3V). Baud 115200. Arnova 10d G3 Firmware Rom
There are several scenarios where you absolutely need to reflash the Arnova 10d G3 firmware: Official firmware files usually come in