It has been a while since i have worked on a 71-73 but i think there is a small tab on the back of the knob that you have to pinch down while pulling on the knob and it will come off. Then there is a screw in center piece that requires a special tool to turn ,but i have taken them out using a pair of pointed nose pliers ,a point in each small notch and using the pliers i turned the center out .The switch comes out of the back of the dash. If no tab on the knob there will be a very small set screw.
It has been a while since i have worked on a 71-73 but i think there is a small tab on the back of the knob that you have to pinch down while pulling on the knob and it will come off. Then there is a screw in center piece that requires a special tool to turn ,but i have taken them out using a pair of pointed nose pliers ,a point in each small notch and using the pliers i turned the center out .The switch comes out of the back of the dash. If no tab on the knob there will be a very small set screw.