The search for the specific archive "Download MT5510S PB803 1920x1080 Polarine 43PL51STC part08 rar" indicates this is a firmware file for a TV mainboard. The MT5510S.PB803
Once you have extracted the firmware file (often named allupgrade_ms5510.bin or similar), follow these general steps for this chassis: The search for the specific archive "Download MT5510S
Press and hold the or CH+ button on the TV itself (not the remote). The search for the specific archive "Download MT5510S