After you install the software, click updates from up top and update the software and library. You might also want to do the firmware at some point.
After you do that and the program restarts, click on the Advanced tab up top and make sure the show trunked radios systems option is checked.
Since it's your first time using it and you already have the radio programmed you'll probably want to load the info from the radio into the software. From the SD Card option up top choose copy configuration from SD Card.
The library that came with the radio and you used to program it is likely outdated since it is updated weekly. It might be a good idea to check and see if there are any changes. If you load your info before updating the library the software will ask you if you want to update your info after you do the update,
To set rebanding, under the trunked radio systems tab, highlight the system and then the site name. Off to the right you'll see a section for frequencies and site options.
Click on the site options tab. Then from the trunking tables type drop down select custom. Now click the edit button next to it. On the box that opens up click set rebanded and click OK and you're all set.
Also, if you re-import the system and it is marked as rebanded in the DB, the radio will set the rebanding options for you upon import.