Make sure that both ignition switches are turned to the off position. There is one on the engine and one on the control panel.

Pull the ring near one of the wheel hubs straight out, away from the wheel.

Rotate it so that the small roll pin lines up with its slot.

Release the ring so that the lock pin slides into the wheel. You may need to rotate the wheels a little before the lock pin fully engages.

With the pin engaged, it should be very hard to turn the wheels.

Repeat this step so that the lock pins on both wheels are engaged.