On the watch, go to the health app (or the exercise tile if you have it up), select workouts. When you get the workout array, center "walking" on your screen. you will see the animation and settings, underneath. Tap the settings and set your target, and any other parameters you want for the workout. If accessing from the time, select the "more" circle and follow the same instructions. You can also tap the exercise itself and while the countdown is progressing, "settings" will appear on the screen and you can tap it and make your adjustments.
