This did not help. After downloading this dmg and running the installer associated with it I got the notification "The version of iMovie installed on this Mac must be updated through the Mac App Store. Check the Mac App Store to see if an update is available."
Should I delete iMovie and reinstall from the above link?
I don't think that would work.
If you don't need iMovie, you can delete the application or ask your boss to sign in using their Apple ID and hide the update so it won't be presented to you.