How do I re-attach 86-021

I believe the 86-021 spring is held in place with a screw eye at each end. Check to see if the screw eye could be missing or broken at one of the ends. It should be a matter of hooking the end of the spring into the eyelet. That said, I don't have a lot of personal experience with this spring. If you still can't get it to attach, you may want to contact a local Pella dealer.