Update a Lenovo X390 BIOS from a USB drive

I have a Lenovo X390 and I need to update its BIOS.
But I don’t run Windows, and their website‘s only other option is, of all things, a fucking iso9660 CD image.
For a laptop without a cd drive.
I tried extracting the files in the CD image, but nothing came out.
According to every tool I have tried, the image is empty.

How do I extract the update files from this cursed CD image?