Hello Ashley,
The best (and only?) way to get the alu-moldings properly seated into the windshield rubber seal is to do it on the bench. It could possibly be done in situ,
but with great risk of ruining, by denting or bending the alu pieces.
Also use a good quality rubber seal to ensure a good fit for the windscreen, OEM
would be first choice. Some of the reproduction seals I’ve seen are low quality
and not worth it.
Hans K