The "part3" in the filename indicates this is part of a split RAR archive. You must download part1, part2, and any others into the same folder to extract the final .bin file.
Open your TV and verify that the board itself has "P75-338V6" printed on the PCB. Download P75 338V6 1366x768 Major part3 rar
Firmware for these universal boards is highly specific to the panel type and resolution. Using the wrong file (e.g., 1080p firmware on a 768p screen) can "brick" your TV, making it unbootable. The "part3" in the filename indicates this is