When trying to update a bios from an USB pen, probably you will need FAT16 or FAT32, to do this from macOS try:

diskutil partitiondisk /dev/disk3 1 MBR "MS-DOS FAT16" "NONAME" 0B
  • /dev/disk3 - disk device to be partitioned, found with 'diskutil list'
  • 1 - number of partitions, optional, but if given must match
  • MBR - partition Scheme (eg, DOS=MBR, Mac=GPT)
  • MS-DOS FAT16 - partition type (or fat32) *
  • NONAME - partition name
  • 0B - partition size (0B=maximum)


sudo newfs_msdos -F 16 /dev/disk3s1

See more: https://pbxbook.com/other/dosfat16.html