I didn`t have success after I tried to solfe the problem with the known tutorials.
I installed on different PC's with Windows 10 the USB driver and tried different Intel flash tools.
The tablet is in DNX fastboot mode and there is no chance to get connection to the PC. The manager won't show a portable Device, no unkown device, ... .
I tried to flash parts through TWRP - ofcourse without any success. The tablet is now starting with the not needed Windows patition and no more with the wanted android partion. Fastboot is possible and I don't have any more ideas.
I should be still in waranty with this item.
What could I do next. I'm not willing to spend a lot more time on a not really working item.