Download the following software package from Fujitsu:

D3003-S1x - Admin package - Compressed Flash Files

Obtain it here:

https://www.system-rescue.org/Download/

use unetbootin , Balena Etcher, dd, emacs, vi or an electron microscope to put it on some kind of media to boot your S900 from

Unpack the files obtained in Step 1 to your boot medium

flashrom -p internal

this should tell you if compatible programming hardware was detected and what kind of FLASH ROM was found.

 Note which detected part numbers match the FLASH ROM on your motherboard best for the next step.

Save FLASH ROM contents as a backup for safety (or is it perceived safety? When the device is bricked, it will not run flashrom anyway. Ah, whatever... Thou shalt make backups.)

flashrom -p internal -c "MX25L3206E/MX25L3208E" -r /path/to/yourfile.bin -V

flashrom -p internal -c "MX25L3206E/MX25L3208E" -w /path/to/D3003-S1.UPD -V

This screen will give you some hacker cred, show it to your friends on every occasion: