Shower door off track

Usually the bottom of most framed doors has a chanel which contain door sweep or hollow gasket,all you have to do is pull it and slide the new one in the same place.
Please note that some times the end of the chanel is crimped to prevent the gasket to move in and out of the track.
I hope this will help.

most shower doors are held in by the rollers some are adjustable if yours arent check to see if the spring is still holding wheels out firm if not spring probably broke

The top rollers should have adjustments on them to bring the door to horizontal as it swings accross the track.

Start with door in the middle and adsust by seinging it to both sides.

Please clarify - you said it's a pivoting door but also said it doesn't slide smoothly - can't really do both at the same time. If it's a typical bypass sliding door then you should be able to make an adjustment to the hanging brackets on the offending door to raise it up off the track. If all else fails the header track can be raised thereby making the doors hang higher and off the track attached to the tub surround.

Try looking at shower door suppliers, and glass companies that make shower doors.

Some times it's possible to tweak a roller track (barely bend) at the proper spot to prevent the roller from back tracking past that spot.

not sure what you mean when inside door "swings" on a "sliding" door,...i'll assume you need the "inside door guide", a little plastic piece that screws with one screw to the main threshold,.....

curved cut glass will not always be the exact dimensions though they may look identical there should be several set screws on both the door glass frame and the shower glass frame that can be loosened and reset to make the door fit and close and open more properly without seeing the showwer itself i can not tell you exactly where they are but they should be either visible or behind a facade piece of metal frame

no you need to replace the door,they are factory pressed.