Please find the latest FW at:
https://www.supermicro.com/wdl/driver/SAS/Broadcom/3908-3916/Firmware/3908/AOC-S3908L-H8iR(-16DDor-32DD)/
To update please just under UEFI Shell run : UPDATE.NSH
Please may refer to update procedure we have :
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Standard Firmware Update Procedure under UEFI Shell
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1. Save the firmware update package to your computer.
2. Extract the files from the UEFI folder of the BIOS package to a USB stick.
(Note: The USB stick doesn't have to be bootable, but must be formatted
with the FAT/FAT32 file system.)
3. Plug the USB stick into a USB port, boot to the Build-In UEFI Shell, then start the firmware update:
Shell> fs0:
fs0:\> cd [FW folder]
fs0:\UEFI> UPDATE.NSH
4. Do not interrupt the process until the firmware update is complete.
5. Perform an A/C power cycle after the firmware update has completed.