Here are some things you can try:

1. Make sure the volume is turned up on your Smart TV using the remote control.
2. Check the audio settings and ensure that output for audio has not been set to MUTE.
3. Check the audio cables that are connected and make sure they are securely connected.
4. Ensure you have the correct input selected based on the type of device you are using to watch.
5. Restart the device you are using to watch and your Smart TV.
6. Try using a different source, such as another device, to ensure that the source is not the problem.