Copy the file to the root of a FAT32 formatted USB drive.
Once you have both part1 and part2 of the .rar archive, do the following:
This is a common source for these specific board-level files (MSD6486T TP.MS6486T.PB753). You can check their firmware file listing for the exact archive you mentioned. 3. How to Update via USB
If official support is unavailable for this older model, technicians often use community-driven databases. Note that these files are often split into parts (like "part2.rar") and may require a paid account or specific community credits: