After the application has been downloaded, you have to pair the device with the software. Luckily, there is a detailed tutorial guide on the official website of the developers. There is also a section for users that have previous data.
Access the following link and read all the instructions on the page: http://www8.garmin.com/fitness/getting_started_ant_tc_mac.jsp
Note: I believe that you also need an account on their website in order to upload and restore the data.