To find it, you need to:
1. Identify your specific Oldsmobile model and engine. This information is usually on the driver's side dashboard, or on your vehicle's registration.
2. Consult a repair manual specific to your year, make, model, and engine. This manual will have diagrams showing the exact location of the oil drain plug. You can find these manuals online (often as PDFs) or at auto parts stores.
3. Look underneath your car. Once you've identified the engine type, you can generally expect to find the oil drain plug on the bottom of the oil pan, which is located under the engine. It's usually a bolt-like fitting. Be cautious when looking under the car. Use jack stands for safety if you plan to work underneath.
Without knowing the specific model and engine, I cannot provide a precise location. Attempting to locate it without this information is risky.