The small spot is the Neutral position.
The other 6 big spots are for gears 1 to 6 (Rocket transmission only has 5 gears though and won't shift further than 5th)
The brass pin should have the spring underneath/behind it in the hole.
It keeps the pin pushed outward to make contact with the spots on the GPS.
You'll have to grasp and pull that pin out if the shift shaft (the shift shaft turns when you change gear), clean it so it slides easily in and out of the hole, and put a small spring behind it. Maybe a biro pen spring or part of one will do.