You can only edit a shared movie by opening the original project. I assume you have deleted the project. If that is the case the only option is to restore the library from backup such as time machine. You can create a new project and import the movie into it. You can then add media, cut sections add titles etc but that's about all. The movie is just a video clip and you build a new movie.
I'm very much of a beginner, but it sounds like once one has made a complete movie, it can't be totally edited? For example, I had put titles in a number of places, but one of the titles had the generic "title and text" still written in it. I had changed it and when I played it back by hitting the space bar, the name was there, but then after saving it to a flash drive, I opened to play it and the title had reverted back to generic and the specific title I had given this clip in the movie had just vanished into thin air. No idea why this happened on just one of the titles but on none of the others. I wanted to correct that, but don't know how. Each title is supposed to have the name of the person speaking on it, but for this one person it says "Title and text" underneath his name instead of his real name. It's pretty frustrating as I don't have time to re-create a whole new movie.
Unfortunately the only way to re-edit a shared movie is to open the original project in iMovie and make your changes. As I said previously there are some limited edits you can make but titles is not one. One should not delete a project from iMovie until you are sure the share movie is exactly what you want. I don't know why the title would play ok in iMovie and fail in the share. Is the flash drive formatted for Mac? Did you save it anywhere on your computer as well? The only suggestion I can offer, other than to restore the library from backup, is if you have the media then import the movie into iMovie and add the same clip and new title as cutaway clip above the original. This may prove hard to align precisely but you could give it a try.
In what version of iMovie?
how can i re-edit a movie already finished?
