The way you flip a video that is upside down in iMovie is really simple. Here are the steps:
1. Click on the clip that you want to flip.
2. Click on the crop icon.
3. This will open your video in the top-right part of iMovie. You will see two arrows at the top of that window next to the word crop. They look like a left and right arrow. Click on one of those arrows until the video has been flipped the right direction.
4. Click done.
Your clip will now look the right way.