Phil,
If it is a separate item, it could be just a friction fit, pry it off.
Before you do that, check and see if there is a set screw holding it, may be on the bottom of the knob!!
Fred
Husqvarna STE927(11.5HP) snowblower, MTD Pro Series 18/42 Lawnmower, MTD 6.5 HP Self Prop Lawn Mower, Weedeater 1500 Blower, Web Gensis 2000