Firmware required for unidentified Android 21.5 Inch All in One PC

[xga]

Hi Guys,

I hope someone here can help me!

I have an Android 21.5 Inch All in One PC using a RK3399 chip that has become corrupt and I need to find the firmware of it to perform the factory restore process (connecting it to another computer via USB and using the Rockchip application to write the firmware file to it). I've managed to find the device online (see link below), but they do not list the firmware.

https://portworldsolu.en.made-in-china.com/product/TdBQxDnlsrVo/China-Android-21-5-Inch-All-in-One-PC-Touch-Screen-Industrial-Tablet-Poe-Advertising-Player-Rock-Chip-2GB-16GB-Available-with-NFC.html

Below is a photo of the motherboard. The only markings I can see are "AD-K28 V1.2" but I'm not able to find anything on it.

Would anyone happen to know what firmware I might be able to try with this All in One PC without bricking it, please?

Thanks in advance for any information that you can share.