With the rubber gasket lubed, push the glass into it towards the center post. It is unlikely you can push its entire width all the way in so try to get the inside center of the glass in the groove along the post and into as much of the horizontal top and or bottom grooves as reasonable. You may only succeed in getting a lot of the top or bottom in the rubber groove along with the vertical part at the center. Then using the nylon tool work the rubber groove around the glass starting at one point and continuing around.
The outside curverd part of the glass has to be pretty much lined up with the gasket groove. If the windshield is not seated in the groove at the center post it is unlikely you can slide the whole windshield into the groove from the outside end without breaking the glass.
If in doubt practice on the broken windshield.
I hope this helps because it is hard to describe but when you have the glass in hand you will see what I mean.