Vent knobs

I have replacement knobs for the outside air vents & am not sure how the old ones come off, any comments would be greatly appreciated

I put some of them on my car a few years back and had to thread the ends of the cables where the old went on, I had to break the original plastic ones off as they were factory installed and not meant to come off. some of the replacement knobs have set screws which would make them easier to install.
You might want to check with the supplier to see what they recommend.