Insert the USB into the TV's USB port while the power is off.
You can download the firmware and access related support documentation through several community-driven tech blogs and forums. This specific board is a common Android smart TV mainboard often found in brands like Skyworth and other generic LED TVs. Direct Download & Blog Sources Download CV338H A50 1920x1080 USB Tested part04 rar
The indicator light should blink rapidly, signifying the update has started. Insert the USB into the TV's USB port while the power is off