Two of the appropriate left-handed screws were supplied in the kit this year, though, admittedly, they were easy to lose. If I recall correctly, they were packaged in a small, clear plastic bag. I don't remember if they were packaged individually or together.
There is a hole in the hex coupling where this screw fits, and then screws into the drill output.
If you do not have or cannot find those screws, and you are sure that was the problem you were having, you can just go buy some.
The specs for those screws can be found
here .