1. Please first check if your TV supports the standard HDMI-ARC and if the sounddeck or soundbar is also connected to this port. The port is usually labeled with eARC or ARC on the TV.
Here, for example, it is HDMI port 2:
2. If the port is present, please check whether your HDMI cable supports at least standard 1.4 or higher.
3. If your TV does not have an HDMI port labeled with eARC or ARC, please use an optical cable to connect the TV to the soundbar/sounddeck. This requires that your TV has an optical port.
4. Some TVs have a separate audio output setting that needs to be configured when sound is played through other speakers such as a soundbar. Please check your TV’s settings menu for an audio output setting.
If such a setting exists, make sure it matches the type of audio connection used (HDMI-ARC or optical) and that the TV speakers are turned off.
5. Also make sure that in the sound settings of the TV (or the set-top box such as satellite receiver, cable receiver, Apple TV, Amazon Fire TV, etc.), the audio signal is set to the correct output format PCM or stereo.
More information about HDMI ARC can be found here