I am indeed using iMovie 9, the version that came with my mini when I bought it in 2015. I am using OS 10.13.3. I appreciate your respective replies very much. Because the Apple support doc does NOT indicate which version of iMovie it applies to, I had no idea that the nomenclature changed from one version to the other.
Jim, when you say that I should drag them (iMovie Projects and iMovie Events) to the root level of the EHD, does that mean that I should NOT drag the folder Movies in which they reside?
The Apple support doc also says that once this procedure is complete, if I want to work with the EHD as the regular location for my iMovie files, I should then "drag the original file in your Movies folder on your Mac to the Trash." To translate for my version, I should then drag the Movies folder or the two folders iMovie Projects and iMovie Events?
Thanks again for your perseverance. I am trying to mark your replies as "helpful" but that option seems greyed out ...