2005 Suzuki Forenza O2 sensor

Have you located the sensor? Do you have the replacement in hand? Do you have tools? The sensor should be located in the exhaust stream either on or very near the exhaust manifold. It will require a 22mm wrench or a special oxygen sensor socket to remove. Disconnect the wire(s) and remove the old sensor. Install the new one and do not over tighten it, it does not need to be super tight, just 1/4 turn after it is finger tight or enough to crush the new gasket on the replacement sensor.