pop the button, but from the backside...turn the wheel over, support the hand ring leaving the center button free/open, push/pop from where the stud will enter the wheel.
careful for the horn wire
Your welcome.
BTW, some horn buttons have, on the backside, a slot that you could use to lift/pop (w/screwdriver...) from the front. Look to see if you have that type and determine where it is from the front. Once it's back on, you will have less change of marring the button when removing it.
Jon