Boot camp assistant can only change disk1 I'm trying to setup and iso file on a flash drive from my macbook using the Boot camp assistant.  It recognizes the iso file, but I am only given one option of using it on disk1 of my own computer and cannot change this to my flash drive.  How can I give Boot camp assistant the ability to recognize the external drive?

I'm running High Sierra 10.13.2

For reference, the iso file is for the windows 10 os.
Bootcamp doesn't have the ability to install Windows on external storage. The Windows installer itself can't install Windows to external storage either, so this feature can't be inplemented to Bootcamp.