Audio & Left side USB fail on Mackbook Air Mid 2013
If trying to use the Audio Midi Setup (as suggested in comments by Tetsujin) doesn't help, your next step would be to run Apple Diagnostics.

Run Apple Diagnostics 

Follow the steps below to run Apple Diagnostics: 


Fully shut down your Mac 
Restart your Mac 
Immediately press the D key and keep it down until you see the Diagnostics screen appear 
Wait for Diagnostics to finish (this typically only takes a few minutes) 
Once complete, one of two things will appear on the screen: 


a No issues found message 
a brief description of any errors found plus further instructions 

If the diagnostics test does find errors, take a note of what they are 


Note: If pressing and holding the D key at Step 3 doesn't work, start again at Step 1 and, at Step 3 press and hold both the OptionD keys instead. This will try and run diagnostics from the internet instead, so you will need to allow more time for it to complete. Regardless, take a note of what happens and let me know how you went.