You need to contact Samsung through the wearable app to arrange a repair. But while they may be quick to take it in and "repair" it they probably won't actually repair it before sending it back. My Fit2 has been in 3 times and they can't find anything wrong with it so I have been "blue ticketed" which means I'm a nutter who has nothing better to do! 43 mins just standing still in a swimming pool !!?? GOOD LUCK 
