I need to get 5/8" into the framing 3" high at the base of my wall framing; Is there an easy way to do this?

In the picture below I need to push the shower base like 5/8" into the frame at the top of the picture
The shower base is 3" high
The framing is a mess as it hosts the piping for the old shower and sink and a big now empty space after I relocated an air vent

I need this because a preliminary attempt to see how the things fit together shows me that the cabinet overlaps the shower pane 5/8"

The shower base edge where the glass gets installed is 2 5/8" so I will be left with 2" to install the glass which could be tight

Update:
The installation instructions are here
https://www.us.kohler.com/webassets/kpna/catalog/pdf/en/1185992_2.pdf
And here are some details relevant to what I am trying to do
It seems that I am going to have to rebuild the frame as pushing the base under and into the existing framing will not allow me to install the two sheets of drywall as instructed