The plan is to move the fixed panel back toward the wall, by tapping it carefully whilst protecting the edge of the glass. You you not want to break it.
As mentioned above, it is easier with the door out of the way.
Use a soapy solution, or CRC or WD40, applied around the edge of the fixed panel. Be sure to lubricate both inside and outside the shower.
Next, use a sharp flat blade, such as from a Stanley box cutter or similar, to loosen the seal around the glass. The blade should be pushed into the joint between the glass and the plastic seal strip. Again, do inside the shower, and outside. This is done so the glass is able to be moved with the next step.
Use a piece of softwood, or several layers of towel to protect the glass edge. Then tap it lightly on its edge to have it slide back into its original place. Start with light taps. Use a rubber mallet if you have one, but still protect the glass edge.
This should result in resetting the gap to the shower door, and fixing the issue. I hope you can get the shower door back in place in one piece.
Disclaimer: This advise is given freely with no responsibility on the part of the writer.