It's kinda tricky to get on, the spring that is. I usually install, make sure the little bend it propped behind the metal stopper on the frame, and then use pliers to pull the part of the spring "the L you could say" that sits behind the brake pedal around to add tension/spring. From there you use the adjuster spring that pushes against the brake pedal to set the height, too high and it will rub against the cover.
Keep in mind, if you look at a fiche page it makes it look like the spring goes on the outside of the brake pedal, however it actually sits in the inside, closer to the swing arm.
It just takes some sitting and looking at it to figure it out, trust me I was in the same boat as you. I had not seen it installed b4....