Sometimes the office of the CEO has someone who acts on behalf of the CEO. They read letters that are sent to the CEO with problems and route them to the right people to get the problem fixed. If it's reasonable, this works sometimes since the request comes from the office of the CEO and no subordinate wants to get in trouble if it's a simple problem to solve.
That said, the luck that I've had in the past is to look up contact details on their SEC filings. If you are a student, sometimes they may give you more attention. I got to interview the CEO of 3M when I was in university using this technique.
To answer your question, you don’t, mostly. He might answer sometimes, as Jobs did, but it’s not normal or expected.
This also depends on the “why” that goes with your question:
If you just want to talk to him, good luck. If you want to serve legal papers, there are other methods that aren’t so much “contacting” him. For nearly anything that one can expect you might want, emailing that address or sending a message via the FAX number you were given is the closest to “executive customer service” you’re likely to be able to get.