Help...how to remove the headlight knob

Depending on year model, that release button will be on the right side of the switch or on the bottom. You'll need to disconnect the battery cable too. Remove the one screw that holds the fuse box in its bracket . Push the fuse box up and back. It will rest behind its bracket. Pull the switch stem to its full on position, push the release button and pull it the rest of the way out.
Do not push the button when reinstalling the stem. That would wreck the catch. The stems tapered end will guide it in past the catch.