Select the workouts you want to simulate (for best results they should be over the same course) then:

• Select "AR - Send <n> activities to Routes View".
  
• In the routes view, select the "AR - Earth" maptype.
  
• Use the play/stop/faster/slower buttons in the bottom right of the screen to control the simulation.

Also use this page to Export Routes to a Garmin Fitness Device.