First, call a licensed and qualified plumber and a licensed and qualified tile contractor. Many plumbers have tile contractors they can recommend.
This is not every step, but these steps should be sufficient to give you an understanding of what needs to be done.
Remove the tile shower floor and the tile on the shower walls up about 8″-12″ above the shower floor.
Remove any damaged wall areas behind the tile.
Remove the shower pan which is now exposed.
Replace the damaged wall areas that were removed.
Replace the shower pan.
Replace the tile shower floor and the tile areas on the walls.
That is a simplified process. Make sure your plumber gets a plumbing permit for this work from the building department in your area.