I never added a ship set style to my Xindi faction. If you are trying to convert it to a civilization than you will need to create the ship set style yourself from the Xindi ships on my workshop and re-save it.
This can be done by copying and editing the faction in the civ builder editor under the Fleets tab. Before you start make sure that all ships you intend to use are saved as ship templates so they can be selected from the selection menus make sure to re-save the civ when you're finished. Keep for your personal use only. Do not share it on steam workshop without my consent please.
Hope this helps and thank you for the compliments, Glad you like my work.