Can a pizza stone be fixed after soap has been used to clean it? We bought a pizza stone from a thrift store (so at least it was cheap). Unfortunately we cleaned it with soap before reading up on how to clean them. I know, rookie mistake.

Is there any way to fix it or should I just toss it out and consider it a lesson is researching new tools before messing with them? Obviously, I have no idea if the prior owner misused it so this might be a lesson in not buying used stoneware.

I haven't tried baking on it since using soap on it and the soap was only lightly used. I guess I should perform an experiment and find out if it makes things taste soapy.
I would rinse well with clear water.  Allow to dry thoroughly, and then use as normal. 

There is a small chance that your pizza stone will impart a soap flavor to your pizza, but I would say that it is worth a couple of pizza cooks to determine if there is a long term problem.  It's really not that much of a risk.