If you have the contents of the Win7 iso already correctly copied to the jump drive, then all you need to do is make it bootable. In the instructions, they kinda mention this, but it's not very clear.
To make the USB device bootable, you need to run a tool named bootsect.exe. In some cases, this tool needs to be downloaded from your Microsoft Store account. This may happen if you're trying to create a 64-bit bootable USB device from a 32-bit version of Windows. To download bootsect:
They recommend downloading bootsect. But there's other tools that will do the same thing easier than bootsect.
Try this to make it bootable: http://www.megaleecher.net/Make_Bootable_USB