MacOS – Why can’t I update the imovie

Bare in mind only footage shot with an iDevice can be edited on iMovie for iPad. That being the case, it's just a matter of finding the correct format.

Wired has dedicated a whole article to this specific matter.
Basically it comes down to convert the video to a specific MP4 with the H.264 codec. You can do this by following these easy steps.

1. Convert your movie to .mp4 on your Mac (if it isn't already in this format)
2. Convert your movie to an iMovie movie with the 264 codec
3. Use iTunes to transfer you movies to your iPad

Normally your files should appear in the iMovie project dashboard.

So thank you to @GeorgeGarside for helping me understand where the problem would lie I was able to find an informative article on correcting the problem

1. Go to the Finder.
2. Hold down the Option key and click on the the Go menu.
3. Select Library.
4. Look for the Application Support folder. Open it.
5. Look for the Dock folder. Open it.
6. Locate files ending in ".db". Drag them into the Trash.
7. Go to the  menu and select Restart (or log out if preferred).
8. Click on the Restart button (or log out).

Source: http://www.imore.com/how-reset-launchpad-mavericks