This is a common failure, and is one that many of us can repair at home. You
will need to make a trip the dealership to buy the parts, but the
counter-person will be aware of the parts you need.

When the roof is tilted up in the back, you can look from the driver seat
along the bottom of the roof panel over the passenger seat and you will see
3 Torx screws (I forget the size, but I'm thinking they are 10 or 20).
Remove these screws, then move to the passenger seat and remove the same
screws on the driver side. Now you can lift the glass out, then jockey the
slide-panel around and lift it out as well. (The slide panel can actually
come out without taking the glass out, but the glass must be removed to put
the repaired slider back in place.) The plastic parts that the dealership
will have sold you only fit one way. When you reinstall the glass panel, you
must take care to make up-and-down adjustments so that it seals against the
car when closed.

PS
I told you that the first step is to tilt the roof open, but on second
thought, I think you can get at the torx screws even with the roof closed
because this is how you will adjust the up-and-down position so that the
glass closes properly. The final adjustment may be easier if you have a
helper that is watching the panel position from outside the car.