Cant update firmware of Dell Wyse 7020

Hello, im downloaded the newest SUSE linux image for my 7020, and successfully push it to the USB 16Gb. After boot i saw

" GRUB loading, welcome to GRUB.

error: no such partition. 

Entering rescue mode"

I repeated this thing with ThinOS image -  and got similar result.  Give me an advise, please, im tired

Thanks for attention.