You have a legacy/discontinued/unsupported DESKTOP BOARD, not a NUC.
This is your forum: https://forums.intel.com/s/topic/0TO0P00000018NEWAY/desktop-boards
And, as the announcement in the desktop boards forum says, the drivers and bios for these boards have been removed.
Unless another forum member has the .bio file, you can try some site like softpedia.com. Careful, some of the driver download sites may have unexpected payload in their packages.
Now, the really bad part is the the bios release notes have been removed, so you do not know what the latest bios is, or any dependencies in upgrading your bios.
BIOS updates will not make your computer faster, they generally won't add new features you need, and they may even cause additional problems. You should only update your BIOS if the new version contains an improvement you need.