If you are talking about the knob on the top of the shift lever, you can change the position of the knob by turning it. It may take some pressure, but it will move. If you can't do it by hand, wrap a cloth around it(to help prevent damage) then use pliers that will open up enough to fit around the knob to give you the torque you need.
If you are not comfortable doing this, take your truck to the dealer and let them fix it.
