How do I fix my headlight switch?

Ditto for what @jayeff has said; we'll need to know the year and any relevant submodule information in order to look up the correct wiring diagram for your rig.

Also, of course the first thing to check is the bulbs; it would be rare for more than one to go out at the same time, but not impossible. You might have not noticed one bulb out and had the other one go out later, for example.

Do you have daylight running lights? If so, do they work? How about your high beams; do they come on? What about tail lights and parking lights?

There are several areas that could be the source of the problem; off the top of my head I'd list bulbs, fuses, wiring, headlight switch, headlight relays and, at least on one wiring diagram I saw for a 1999 Ram, something called a Daytime Running Lamp Module on the left inner fender.

A voltmeter or 12V test light will be a valuable tool in figuring out where the problem lies.