It may require a bit of mechanic work, but this is the basic procedure. You will need a digital voltmeter to track this down. Check for voltage at the horn, when the button is pressed. If there is voltage, the horns may be bad. This is fairly common.
If there is no voltage at the horn, check for a signal to the horn relay, again with the button pushed. You may also try swapping the horn relay with another relay, several are the same part.
If not you you would need to check for voltage to and from the switch. This is part of the air bag, and we have replaced several of these, for this problem. Some folks also fashion a separate horn button, due to the expense of air bag replacement.