Take your time, read the instructions twice, and you will be rewarded with a more stable, more capable, and more enjoyable DMR experience. Your DM1702 has hidden potential; a firmware update is the key to unlocking it. Disclaimer: Flashing firmware carries inherent risks. The author is not responsible for bricked radios. Always verify hardware compatibility and download firmware from official sources.
Run the loader. It will detect your radio in DFU mode. Select the OpenGD77 firmware file (for the DM1702, not the GD-77). Click "Write to Flash." The loader will first erase the stock firmware, then write the new one.
This is the critical step. Turn on the radio while holding the PTT (Push-to-Talk) button AND the Monitor button (the top button on the left side, just above PTT). Hold them for 3 seconds. The screen will remain blank, and the LED may flash. Your PC should make a "device connected" sound.