quick sensor question

hey every 1 I'm fairly new to working on cars but have been told the knock sensors on the motors are easy to replace but was wondering a few things

stupid question but my left sensor is faulty but how do you tell which one is the left? is it from standing at the front of the car or from sitting inside of the car?

also will I have to take it to a mechanic to clear the codes after ive put the new knock sensor on or should the check engine light/warning clear automatically?

any help or tips for doing the job would be appreciated :)

cheers!