With the following pieces aligned carefully set the gear assembly into place:

Avoid rotating these pieces to maintain alignment.

As you set the assembly into place, make sure the two stop-screws are on the left side of the black plastic stop.

Align the large peg with the wide slot.

Align and the small peg with the small slot.

Press down on the gear assembly to snap it into place.

Once in place, rotate the coarseness knob through the full range to make sure it's all working.