You'll need to look carefully near the bottom of the radiator and along the front of the engine block. Sometimes there's a grommet or hole in the area where the cord exits the vehicle. A flashlight might be helpful.
Important Note: Not all 2002 Oldsmobile Aleros came with block heaters. Check your owner's manual to confirm if your specific vehicle model is equipped with one. If your manual doesn't mention it or you can't find a cord, it's likely your car doesn't have a block heater.