For a completely dead PCB where the MCU is unresponsive:

To proceed, physically inspect your device:

Once you have obtained the correct nm368818 firmware link and downloaded the file (usually .bin, .hex, or .dfu), follow this generic flashing procedure. Adjust steps based on your MCU type.

If you bought the NM368818 from AliExpress, eBay, or Banggood, message the seller directly. Provide your order number and ask for the “latest firmware HEX or BIN file.” Legitimate sellers keep backups.