Newbie lesson learned: now how to fix it?

[Hanbin Y.]

Hello BPers, I recently closed my first 5-unit apartment in Cleveland. I did not realize until today (when I called the power company) that the previous owner has owed a few hundred dollars of electric bill before closing. I admitted I did not check thoroughly. I was only focusing on an estimate of utility charges because it's supposed to be paid by tenant. Anyway, I already improve my checklist for future purchase. Now how do I deal with this situation? 

Thanks!