Files like these are often hosted on specialized technician forums or repair repositories:
TP.MS638.PC822 , a common dual-core Android TV mainboard supporting 4K resolution. Resolution: 3840x2160 (4K Ultra HD). Download MS638 PC822 3840X2160 REF56 CONTINENTAL part2 rar
Usually, the extracted file (often named allupgrade_638_sos.bin or similar) is placed on a FAT32-formatted USB drive. You then plug it into the TV and power it on while holding the power button to initiate the "USB upgrade" process. Files like these are often hosted on specialized