Hi, Pierre34 please follow the steps below.
1. From the home screen, swipe either up or down to access apps.
2. Select Settings.
3. Select Sounds and vibration.
4. Select Notification sound.
5. Select preferred Sound.
Hi, Pierre34 apologies for the inconvenience caused, kindly be advised that the functionality to use downloaded notification sounds is not available, however, Samsung appreciates your input and our team of experts will look into the possibilities of improving the product functionalities.