Try..
scroll to your activity...
long press menu/up button...
scroll to training....
choose training calendar....
this is how to reach it on my 5x....
I set it up so that it is a widget. The widget allows you quickly see your next or upcoming activity (and past workouts). If you want to run the current activity, you just select it - and then select Do Workout. It will then ask which of your activities you want to use (like Running or Treadmill).