Snow makes a whole city quieter without saying a word. Some people have that effect too.

Calm is contagious in the same way panic is, and it moves without anybody announcing it. Someone walks into a tense room and the volume drops, not because they took charge but because they are not adding to the pile. Presence can be a contribution all by itself.

Notice who has that effect on you and spend more time near them. Then try being that person once this week, in a situation where you would normally match the energy of the room. Slowing your own speech does more for a tense group than any advice you could offer.