shower door frame not level

[long thi]

Need to reinstall shower pivot door frame, but the issue is I removed some material that helped the frame be leveled. I removed it because it was cracking and I thought i didn't need it. I wanted to recaulk the frame because the wall around the shower was cracking and having bumps, probably due to the steam coming out of the cracks of whatever it was that was helping the frame get leveled. any other suggestions will be welcomed. I thought about using spray foam to help make it level but unsure about that idea

also want to say that this material feels like rubber

 

[Reach4]

Can you push shims into place before tightening the screws?