[Phx Mike]

You need to get an “ignition ring nut removal tool” - it has fingers that will align to those slots on the collar of your switch so that you can keep the whole switch from rotating while you unscrew it from the back. I saw some online but they come in different diameters and with different number of fingers.

When you replace it consider getting one that just has a knurled collar that you can hold with your fingers or soft jawed pliers.

Mike