Stand facing a step or stairs. Hold onto a banister rail if that is available.
Step your operated leg up on the step as shown in the first image. Bring your unoperated leg to join it as shown in the second image. Gradually place more weight on the knee as you feel comfortable.
Turn to face down the step or stairs.
Now step the unoperated leg down first, then the operated leg to join it. You may hold onto a banister rail if this is helpful.
Repeat 10 times.
To make this harder, either slow down the step up or step down so you are making your operated leg work to control the task.
Increase the repetitions.
You can repeat this with your unoperated leg.