Right-click on the speaker icon present on the taskbar.
Open "Sound settings".
Under "Choose your output device", make sure your Kogan TV is selected as the default playback device.
Click on the "Properties" button for your Kogan TV (optional). Here you can check if the sound is muted or adjust the volume level.
Update Audio driver.
Open your device manager, expand "Sound, video and game controllers", right-click on your audio device and select "Update driver". Choose "Search automatically for updated driver software".