It has been a long time since I have taken my speedo assembly out. But you may have to drop the steering column down. For sure, you will have to disconnect the speedo cable from up under the dash. I know there are two screws at the top of the bezel you have to remove and a couple at the bottom. Anyway, you said the shift indicator doesn't move so something has become unhooked from the shifter. Here are a couple pictures of a speedo cluster I have that has the hardware that hooks onto the shifter assembly. Once you get it out, you will see what is broken or missing. Shouldn't be too tough of a job. Let me know if you need any of these parts. You may be able to drop the steering column and not have to take the speedo cluster out if you can get to the two screws that hold the shifter indicator in.
View attachment 379367
View attachment 379368