That's a Mac issue, not a Garmin issue. Usually it is just an association issue. So you need to re-associate the .pkg files with the installer. Here is something I pulled off a google searh:
First right click on the .pkg & select the get info. New window will appear, select the open with, Is there Installer app from the list to chose from?
You can manually open the installer app from:
Is the installer app location there?
Hope that helps.