What if I can't make my California small claims hearing date?

Request a postponement, called a continuance, from the court clerk as soon as you know there's a conflict, and do it in writing with a stated reason. There's usually a modest fee attached to this request.

What you should not do is simply fail to show up. A default judgment, an automatic loss entered because a party didn't appear, is considerably harder to undo after the fact than a continuance is to obtain in advance. If a default judgment has already been entered against you, the form for asking the court to set it aside is SC-135, and there's a 30-day window from the judgment to file it.