Riding mower overfilled with oil

Wait a few days for the excess oil to drain down to the pan. Also, pull the plugs and clean off any oil fouling. Then try to start

Most lawn mowers stop working because of fuel issues. Get a can of starting fluid and see if it fires (even if briefly). If yes, investigate fuel and carb. Disconnect fuel line from carb and see if fuel comes out. If yes...

Examine the carb - some have removable float bowls. Carefully remove and see if there is gasoline inside. If no - needle and seat/float is stuck. If yes, find the main jet and blow it out with carb cleaner. Do not poke the jet with hard/sharp metal tools - its soft brass and you will screw it up.

If you can't get it to fire with starting, first try plugs (sometimes easier to get new ones than clean the old one especially if its oil fowled).