Typically, the firmware is copied to a FAT32-formatted USB drive, which is then inserted into the TV's USB port while holding the power button to trigger the update.
This motherboard is a "smart" universal board designed for high-resolution 4K panels (3840x2160). Technicians often look for these split ".rar" files (like part 20) to: Download HV553 PC821 3840x2160 Ref56 part20 rar
If you're looking to purchase a replacement board or find verified software, reputable retailers like AliExpress and Amazon often stock the original hardware and provide basic documentation. Typically, the firmware is copied to a FAT32-formatted