How do I update the BIOS using the Flash BIOS Button?
Download the latest BIOS file, rename it to MSI.ROM, save it to the root of a USB storage device, connect power to CPU_PWR1 and ATX_PWR1, plug the USB into the Flash BIOS Port on the rear I/O panel, and press the Flash BIOS Button. The LED will flash during the process and turn off when completed. (Page 50)
From the official Msi B550-A Pro Motherboard manual, page 50
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