Insert the USB into the TV's USB port while the TV is unplugged.
I must respectfully clarify that does not correspond to any widely known, verifiable, or standard firmware release from a major consumer electronics manufacturer (e.g., Samsung, LG, Sony, TCL, Hisense, or Mediatek reference designs). t.ms638.733 firmware
Because this is a generic board used by various manufacturers, official downloads are rarely on a single site. You can typically find valid firmware on specialized technician forums or community repositories: Kazmi Elecom Insert the USB into the TV's USB port