Dear Lisa I know how to run a Raspberry Pi off a Flash/HDD Drive. I still can not find the "How to Run Raspberry Pi 4 or 3 Off an SSD or Flash Drive" you are refering to. And the quetion is not HOW to run it but HOW to change the operating system without dismanteling the whole setup.. How do I get a new OS Image on the system when its setup and in a case?