I've got a similar or the same problem:
DELL XPS 13 (9350).
Windows 10 Creation Tool
Boot from USB
Unable to reset your pc. a required hard drive is missing.
Today I've been to my university's IT department. At a certain point the SSD showed up in diskpart, then
we could clean it.
However, W10 didn't work after the installation so I'm facing the same problems again.
Now: diskpart -> list disk -> only the USB shows up
What about BIOS? Do I have to check or uncheck Legacy or UEFI in some way?
Also I copied and unzipped the DELL drivers for the SSD onto the USB on which the W10 Creation Tool ist like DELL
asked me to but this time it doesn't work and again, diskpart doesn't access the SSD.