Are you trying to fix a issue, or are you just looking to update the Android version on the board? TP.MS338.PB819 USB Firmware Software Bios Bin
Since you are looking for "part 5," it implies you have already found a source with multiple links. If one link is broken, try searching for the exact filename on:
Much of this specialized "China board" firmware is shared via Telegram channels dedicated to LED/LCD software.
: Creators often link to their own firmware archives in the video descriptions of "How to fix [Model]" tutorials.