On the back of your lift where the pull out for the rear tire is there is an orange or red stud (depending on table color) hanging down about 3/8″ diameter and 3″ long. The loading ramp must be removed to see it. It is to the right of center at the very back edge of the the lift table.
The lift must be in the down position for the wheel dolly to engage the pin. There is a hole in the stem of the wheel dolly, the stem is between the wheels on the dolly. Align the hole so the pin on the lift table fits through the hole on the dolly.
Pull the handle on the wheel dolly towards you and prop the lift up to allow rolling on the front wheels of the lift table and on the dolly wheels.