Find oil drain plug and drain. Replace plug and fill with correct amount of oil. Remove spark plug, ground spark plug lead, and turn motor over a dozen or more times to get oil into bearings. Replace spark plug and spark plug lead, and start engine. If engine has speed control, keep engine at lowest speed. Allow engine to reach operating temperature. Do not load engine at this time. Shut off engine and drain oil while hot. Refill with oil. Mower should be fine for use. After next use, check oil fill for gasoline smell. If present, change oil again.