Download the UEFI-Shell github ISO file UEFI-Shell…RELEASE.iso

Extract the file efi\boot\bootx64.efi file and rename it to BOOTX64.efi (note capitalization)

Format a USB drive to FAT32 

On the USB drive create the following path /EFI/BOOT (note capitalization): 

Copy the BOOTX64.efi file to /EFI/BOOT on the USB drive