Cannot Figure out How to use panStereo

I'm a bit of a beginner. I'm trying to make a script on an audio source that makes the Stereo Pan = 1.0 when the right arrow key is pressed and -1.0 when the left arrow key is pressed. The only issue is I cannot figure out how to access the Stereo Pan variable within my audio source. PS. I am able to play different sound through different audio sources to get the "left right" effect. I just want to change the direction of the audio on one continuous source. Thanks!