Help with tower shower the handle that controls where the water comes from is broken and water is only coming?

from the middle jet. when the handle is at 12 oclock it should come from the overhead one, at 3 o clock the middle jet and at 6 o clock it should come out of the lowest jet but now no matter where it is it only come out from the middle. Can anyone tell me how to fix this prefferably without calling a plumber as i don't have the cash! thanks