Hello, I am sorry that you are experiencing issues. Please allow me to clarify:
The "original image" is the image that is stored to ProShot's local folder. If a picture was taken with ProShot v3.0 or higher, the original image will be saved, along with a second image (that includes filters, etc) that will be saved to the system's camera roll.
If you receive the error message "original image not found" that means that either the photo was captured with ProShot v2.9 or below, or the image was manually removed by the user within ProShot. Uninstalling ProShot, like when uninstalling any app, removes the contents of that app's local storage. In the case of ProShot, this will remove all of the images within its local folder, but it will not touch those that are in your system's camera roll.
To get past the "ISO" part in the tutorial, please see this demonstration:
ProShot v2.9 New Features Overview - YouTube
Simply pull ISO to the left, as the instructions state.
I would like to apologize for the confusion from the tutorial. I will add a skip button in the next update.