If you are holding the trigger in your left hand, looking at the rear of it, use a small flashlight to look inside and you'll see a cavity where the coil of the spring sits. Put the flashlight down and take the spring in your right hand and insert the short leg of the spring first, oriented to the left. That leaves the longer leg sticking out of the back and it should be on the right side of the trigger. Put the hand in just enough that the two pins are inside the trigger, but not so much that the spring leg can't move freely past. The best tool I have used for this next step is one I made myself...very small screwdriver with a shallow notch cut in the tip. But anything will work that you can push that spring leg up past the pins of the hand. Once that spring moves past the pins, push the hand in and release the spring. If you have an older pinned trigger you can compare it to, the function is identical, but with the MIM version you just have to get the spring oriented correctly before anything else. Do it once and you'll realize it's very simple....but I won't lie, it kinda freaked me out the first time too.
