To get the mic audio volume, use Audio.AnalyserRMSLevel("mic", 0) expression.
Note, that it returns negative values from -45 dB to 0. And also, until you press the button to request a mic, it returns -infinity.
So if you want to use this value to move the clown head, you need to make some adjustments:
(max(Audio.AnalyserRMSLevel("mic", 0), -45)+45)*4
max(.., -45) gets rid of -infinity value.
By adding +45 you make the value positive. And multiplying by 4 extends the range, so the value will change from 0 and 180.
I don't know what effect you are trying to achieve, but you can try MoveTo behavior with different speed/acceleration/deceleration settings.