You can find the specific firmware files on technical community sites like Kazmi Elecom , which hosts various versions of the board software.
Place all downloaded parts (Part 1, Part 2, etc.) in the same folder. Use a tool like WinRAR or 7-Zip to extract Part 1 ; it will automatically combine the others into a single folder containing the firmware file (usually named messi.bin or similar). Download P75 338 1366x768 512M NORTH TECH 32SMS part2 rar
Turn on the TV (some models require holding the Power button on the TV panel until the update starts). You can find the specific firmware files on
Wait for the progress bar to finish. the TV during this process. Download P75 338 1366x768 512M NORTH TECH 32SMS part2 rar