If the button doesn’t work, you may have to go to the dealer to get it fixed. If it’s a newer car and you’re at the dealer, tell them that the button isn’t working.
You get to the bottom of it by removing the steering wheel and then the lower part of the dashboard. You then remove the screws from the side of the dash and remove the upper part of the dash. You then remove the screws holding the radio and remove the radio. You then remove the screws holding the stereo and remove the stereo.