If I walked out a store forgetting to pay, how can I get the theft charge dropped?

You will need to hire an experienced criminal defense attorney to represent you if you want to get your theft charge dismissed or reduced to a lesser offense, like "Littering." It depends a lot on which court your case is being prosecuted in, your criminal history, and what they accused you of stealing, but it's very likely that your attorney could get this taken care of without you having to appear in court.