How do I replace my climate control?

The fresh air to recirculate works but it doesn't switch from the floor to the vents to the defrost. Cold winters coming up and I'd like to have a defroster. I took it all apart to find the knob isn't connected to the cable and looks like metal piece is broken or missing. Found part on eBay but when I went to take it out I can't get a screwdriver in there to take cable screws out and it just doesn't want to come out with recirculate cable attached and what other cables plugs do I need to know about? What is the best way to replace these controls? Thanks so much in advance.