I have had the Baggershield fo several years. I think you are referring to where you are fastening the clear section in the upright position. The issue is the same in the reverse as when you reverse it to store in the lowered position..
I switch mine periodically throughout the season and do it now without much thought or trouble. I have found that it helps to slide the section over and on to the center stud first. You can add the plastic nut at this point but loosely. Then flex it from either the left or right side, whichever you are doing next, and guide it over the next stud. Then follow with the other side. Installing on the center stud holds it allowing you to bend or flex the shield. Hope this helps!