The box that the fiber wheel is housed in, is slotted.
So, you loosen the nut that the drive cable is housed in.
It's underneath the gear box.
Once you have loosed the nut, give it a couple of light taps, and it will slid towards the drive wheel that attach to your wheel.
Ideally, there should be just a slight gap between the drive wheel and the bottom of the teeth on the fiber wheel.
That assures that it spins freely without binding.
If you still don't have enough engagement, then you can bend the bracket where it hangs down from the axle.
That hanger, should be against the fork, with truss rods, fender braces etc. outside of that.
Hope this helps, good luck!