Grounding skills help reorient a person to the present to the here-and-now. They are vitals tools to have when you deal with anxiety, flashbacks and dissociation.
Grounding with sound can be as simple as listening for what sounds you hear around you in the here and now. This requires attention directed outward instead of inward where the distress is located. Again, it is important to name the things you hear, either to yourself or out loud.
Other ways to ground with sound is listening to music or nature. Go outside and listen to what you hear around you. If that is not possible, plug into your phone and listen to music that calms you down, or brightens your mood, or reminds you of better times.