What can I do if I didn't process my salsa long enough?
In general, if jars are improperly processed or don't seal, you reprocess them exactly the same way you did the first time. This doesn't depend on the original recipe; you just have to do the exact same thing over again. In your case, since it sounds like your original process was hot pack, you would have to open the jars, dump out the salsa and reheat it, resterilize the jars, and reprocess.

But in your case, unfortunately, it's too late. If you didn't process it long enough the first time, you have to assume that it wasn't sterile, and treat it as equivalent to not canning it at all. Yes, probability-wise, your situation is safer than that, but you have to plan for the worst case, because you have no way to tell. Something may have grown in there. Canning just isn't a good place to mess around with safety.

And before someone chimes in and says it, yes, if you're the kind of person who eats things that have been left out way longer than is reliably safe, you could save it. It'll work out some fraction of the time, so there are plenty of people out there who can truthfully say "I've done this and never had a problem." But it could also get you sick, so I can't recommend it.