Hi,
Backup light switches rarely fail, in fact I can say that in my whole career, I have never changed on of this design.If you have a scanner, hook it up and see if the p/n input is correct.In lieu of that, follow the previous instructions. The switches are plastic, and can be adjusted by hand, slides back and forth.Stick the car in reverse and move the switch until the lights come on.Bulbs could be bad , as an alternative.
Let us know the details on emissions test failure.