This is how you will be able to replace an exercise in a program section.
Step 1: Open an existing program that is filled in with exercises
Step 3: A pop up will appear where you would be able to see the ptEnhance library, STAC library, my library, and my custom exercises. You can pick an exercise among these selections of libraries. Once you have selected the exercise that you want to replace you can click on the replace hyperlink.
Step 4: If you observe the stretches and warm-up section, the exercise Appley Scratch Stretch was replaced with Upper Trapezius Stretch.
That is how you can successfully replace exercises in your program section.