Relieve tension (5,3,3)
I believe the answer is:
clear the air
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">relieve tension</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for clear the air that I've seen before include "Dispel controversy or tension" , "way to reduce pollution?" , "To simplify the condition" , "Lower the temperature" , "Dispel differences" .)