1973 Chevy Nova tumbler

If this is a column mounted switch, there should be a small hole in it. Install the key then turn it to accessorie. While doing that stick a paperclip in it to push the button inand remove the tumbler. If you don't have the key for it and are replacing the tumbler, then get a slide hammer with a small screw on it, screw into the tumbler and use teh slide hammer to pull itout. Then install the new tumbler by llining up correctly and turn to start to install.