Step 1: fix that thing
Also, there is no SDK, you make the 3d models in i.e. blender, then use i.e. sublime text to make scripts for them and then put a the stuff in a zip.
And because you still don't know how to do it I would suggest searching for tutorials, there are lots of tutorials on forums.
You could also open the zip files of other vehicle add-ons, to see what's going on there.