Option 1. If you backed up your FTM2012 file, or chose the option to make a copy when installing FTM2014, just open FTM2012. If you don't see it in the list of files in the Plan workspace, use File > Open > browse to find it.
Option 2: If you have made a bunch of entries that you don't want to lost in FTM2014, you might try File > Export > FTM2012 format and see how that works for you. I would be sure to put in its own directory separate from your FTM2014 file and related media folder, so that the related media folder gets copied, as well.