If you cannot find it via the menu, use the HP support search bar with the exact phrase: "HP USB Imaging Tool for Thin Clients" .
Instead of editing BIOS permanently:
Make two USBs. Label one "Win10 t640" and another "ThinPro t540." Keep them in your IT drawer. One day, they will save your weekend. hp thin client imaging tool usb download
Once downloaded, run the installer on your admin PC. The interface is surprisingly simple, but the options can be tricky. Here is the workflow: If you cannot find it via the menu,