Currently, the two card types in Fundy Designer are Flat or Bifold. However, if you have a .jpg Tri-fold Template from your favorite lab, you can upload it to the software in the "Template" tab of the Card Designer Wizard.
Once you are in the templates tab, you want to select "Flat" as the card type to upload a tri-fold template. You can then "Select File" and choose your template file (needs to be a .jpg)
Happy Designing!