Accidentally turned off "allow access", now can't import media into iMovie

New user to iMovie. I keep my photos and video files on an external drive in my own filing system. I want to create a movie from several videos I took today. I copied the files from my iPhone to my mac (on the external drive). I watched a tutorial on how to use iMovie. The first thing I did was to drag the files to the timeline, but then realized I probably want them first in the upper left part, where it says "import media." I couldn't do the drag and drop to that section, so I clicked on import media. When it asked me for permission to access the desktop and also something else, I declined, which was probably a mistake, I now realize. The desktop appears empty, and when I navigate to the location I put the files, it also appears empty. I even tried copying the whole folder containing the video files to the desktop, but it still is empty. I looked in preferences and everywhere else for a place to change my decision, and cannot find out how to change that. I've googled, but am not finding information about this kind of thing.

How can I rectify my mistake in allowing access, or where should I copy the files so that I can import them?

thanks, Carolyn

edit to add, because apparently I cannot delete this message: apparently I had not selected the correct thing in the panel on the left. Very confusing, but now I have all the movies in the upper left box.