Fill a bucket with water. You will use this to clean your edger as you work. Dip the edger in to wet it before you begin.
Seat the curved edge of the edger between the concrete and the form at one end of the tread. The best way to do this is to make a sawing motion with the edger until the flat of the edger is resting on the concrete tread.
Tilt the edger slightly toward the form and away from you and draw it along the form to the opposite end of the tread. You want the edger to be lifted up slightly in the direction you are pulling it so it does not dig up the concrete.
Lift the edger straight off the concrete. Clean the edger in your bucket of water and repeat these steps for each tread.