I don't believe that they sell just the knob itself. You're going to have to purchase the whole unit which is called an "electronic shift module" or ESM.
There are a couple of videos on YouTube of the swapping out of the module it seems pretty straightforward.
I have same problem on my 2015 Durango. I live in Florida and it's hot so thats the only reason I think it happened. I bought a Mopar replacement just have not replaced it yet. Looking for video. This happened like at 80K