You can download the firmware version 1.58 through Google Search or from the official website if you have an account on their website. However, downgrading is done in the opposite way as you upgrade. Download the flash file, start the software and access the Upgrade module, select the file and begin flashing. This can lead to strange results because there isn't anywhere specified about the procedure. On a side note, the firmware of the Dragon Box reached version V3.33 Beta. You are trying to flash a very old firmware file without support for newer models. Avoid bricking the device and flash the latest version of the firmware.
