You can add labels or custom names to your exercises by clicking on the little "+" sign in the bottom right of each exercise in your workouts.
This will open up the exercise label screen and allow you to change the name of the exercise or add a label to it to suit your needs. Change the text to what you'd like it to display and press the button. In the example below we've changed it to say "10 reps".
The next time you run the workout you will see the labels displayed underneath the exercises on the TV.