Depending on the TV's state, you can sometimes update via USB through the settings menu if the TV still boots. If the TV is dead, you may need an EEPROM programmer (like the CH341A) to flash the chip directly.
The .rar extension indicates a compressed archive. You must first extract the internal .bin or .img file using a tool like WinRAR or 7-Zip .
Dumped flash memory on LG webos 43UJ6300 smart TV, now what?