You have an MTD log splitter with a Briggs 5.5 HP engine you can't find any oil drain plug that exits underneath or on the side of the engine Please advise?

What is the model number of the engine. If this is a newer engine and it is a overhead valve engine, normally the number is pressed in on the valve cover, kinda hard to see. Sometimes it is located on the exhaust debris guard, will be about a 20 digit number. Several of the newer style engines actually have the drain located at the bottom of the dipstick tube.