The fuel filter on a 1985 Oldsmobile Regency is located
in the fuel line, usually near the fuel tank. There isn't a standardized easily accessible location like an engine bay filter for this model year. You'll likely need to either consult a repair manual specific to your 1985 Oldsmobile Regency (with engine size specified), or possibly get under the car and trace the fuel line from the tank to see where a filter might be incorporated.
Be extremely careful when working near fuel lines. Gasoline is highly flammable, and you should always disconnect the battery's negative terminal before working on the fuel system.
