OK well this is probably the most annoying thing you can try to do in this game and it either goes easy or straight to the bin. So you probably know you need to wind the spring up but not the string.leave that loose through the hole. Now using a thin screwdriver, catch that loop on the end of the spring and try to seat it in the groove in the cover.

Now if your having difficulty locating it the you can undo the brass grommet for more access. t
This is a ***** of a job but it will go.

Just make sure there are no kinks in the spring or it'll jam up all the time and dont tighten the screws too much (they clamp the wheel against the case). Threadlock is a must here.