Theft-Loc for Chevy Silverado Stock Radio

I recently changed the starter on my 1999 Chevy Silverado. In doing so, I needed to disconnect the battery during the process, meaning the radio lost power and the Theft-Loc engaged. I purchased the pickup used and do not have the code to unlock the radio. Does anyone know how to reset the the radio? I called the dealer and they said they could do it for $75 dollars. I would rather do it myself.

Thanks for the help.