From Settings, tap Advanced features and select Side key, and then tap Side key again.
Here you can select your desired settings.
For Double press, you can choose between:
- Quick launch camera
- Open Bixby
- Open app (Tap the Settings icon to select an app.)
For Press and hold, you can choose between:
- Wake up Bixby
- Power off-menu (You can also use Quick settings or Bixby.)