LDD.M538.B138 (a common board used in 4K UHD smart televisions). Resolution: 3840x2160 (4K Ultra HD).
With the TV unplugged, insert the USB. Hold the Power button on the TV (not the remote) and plug the TV into the wall. Keep holding it until the software update screen appears or the standby light begins flashing rapidly.
The filename describes the software environment for the TV's internal hardware: