diskpart list disk select disk X (Replace X with your flash drive/SD card number) clean convert gpt create partition efi size=100 format quick fs=fat32 label="System" assign letter=S create partition primary format quick fs=ntfs label="Windows" assign letter=W exit Use code with caution.
Locate your installation media drive letter (we will assume it is drive D: ). Use DISM to apply the Windows 8.1 ARM64 file system directly to your target Windows partition ( W: ): windows 81 arm64 iso install
If you are trying to reinstall Windows on an original ARM-based Surface device, you do not need an ISO. You need the provided by Microsoft. diskpart list disk select disk X (Replace X