Are you using a small (eg, 2-GB) USB that's formatted FAT32? Did you copy the BIOS .exe file onto the USB, not the Recovery .rcv file that's available for download on the same page? Are you plugging the USB into the PC with power fully off?  You can't just do a Restart from inside Windows. Can you get to the F12 menu and open the BIOS Flash Update option?
There is no button to browse the USB drive?
XPS 8930, BIOS 1.1.26 fails to load, #2