Insert the USB into the TV's USB port while the power is off.
: This site often hosts full firmware collections. You can find their dedicated post for the CV338H-A50 Software Download which includes links for various resolutions, though verify if the "part04" split archive specifically is currently active as some older links may expire. 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