Start your session form band of app (offline/ Online). The session timer will start on your band. To use the rest timer you have to go to stopwatch option by using bottom touch button. Press it on right side of the screen to get it started. When your one workout is completed you can start the stopwatch to get the notice of exact time of rest before you start another workout.
To stop it again press the right side of screen.
Please note you can start your stop watch only when your timer is running.