Choose the firmware patch to install on your tablet.
To allow browser access to WebUSB DFU without sudo, configure a udev rule:
echo 'SUBSYSTEM=="usb", ATTRS{idVendor}=="28e9", MODE="0666"' | sudo tee /etc/udev/rules.d/99-huion-dfu.rules && sudo udevadm control --reload-rules && sudo udevadm trigger
After running, unplug the tablet and reconnect it in DFU mode.
Unplug USB cable, hold the shortcut key shown below, and reconnect to PC.
Backup current factory firmware before writing new patch.
Write selected firmware to tablet with full verification.