move imovie library to external drive

Hello, how do I move my imovie library and projects to an external drive without getting a gray screen?

After a hard drive failed one year ago, I brought back the projects from an external drive (using finder) and the screen was grey because it said it could not find the underlying video content. Please note that I did not have a time machine and used the finder to copy from a backup drive.

So there was audio but no video.