In one like post #3, the spring goes in exactly as shown in the picture. It can be a bit fiddly to get it in there in the right place. It can be helpful to use a spray can straw over the long end to hold it with while inserting it.
Once in place in the trigger, the long end is compressed upward with a pin punch, allen wrench, or other tool just smaller than the slot in the trigger, while the hand is inserted. It's best to start the hand partway with the pivot pin before compressing the spring. Once compressed, you can slide the hand all the way in.