How do I take out climate control box?

My temperature control knob feels like a gear is slipping when I turn it. And the temperature of the air never changes. I tried to get in there and see what’s wrong but I can’t figure out how to take the top piece off to look at what’s wrong with the knob. Does anyone have any suggestions?

 

If I remember every thing can be accessed through the back every thing needs disconnected and the whole climate control unit needs to be removed .

If that not possible you might be able to cut the top off and then glue it back together.

I have only ever removed the whole unit to work on them.