1. Format your USB to Fat 32
2. Transfer GTCOMBO_v2.0_C20.A9.1.29_20240620.zip to the USB stick.
3. On the USB stick unzip the GTCOMBO_v2.0_C20.A9.1.29_20240620.zip to the USB stick also.
4. Transfer the latest Mars Firmware Mars_V3.3.3.
Your stick should end up looking like this:
5. Now power down and flip your combo over and insert USB stick i use the side USB port, now either short the points on the motherboard or press the reset button and hold it pressed and power on the Combo while still holding the reset down.
6. Keep it pressed till the Android recovery screen appears.
7. Scroll down and select upgrade from EXT, long press on ok or in my case long left click on a usb mouse brings up a screen to select the firmware to upgrade to. I went straight to the Mars Firmware and selected that long press on ok or in my case long left click on a usb mouse starts the upgrade.
8. When it finished flashing select reboot.
thx Ferret