Basically, in order to reprogram an SSR ECM back to stock configuration you need:
-the original calibration files for your VIN- available on CD for years up to 2007 (if using a GM program) or by paid download from a subscription service
-a PC that can run a software program (such as GM TIS 2000) to manage the files and the transfer
-a professional scan tool (such as a GM Tech 2 or a Tech 2 emulator “Tech2Win”-Tech 2 for Windows) that interfaces to the software program and to the vehicle to transfer the files and reprogram the ECM
Other, more recent professional scan tools than the dated Tech 2, e.g., by other manufacturers, also offer reprogramming options.
Other options: There also are companies that can perform bench programming of ECMs given the vehicle's VIN. They advertise this as a service when selling refurbished ECMs. You might consider contacting one of those companies to ask if you could send them your ECM to be reprogrammed to stock. Or contact a (GM) dealer to have them perform the reprogrammnig on your SSR.