Remove the top engine cover, then unplug the single wire on each coil. That is a coil kill wire that has a diode for each coil made into it. Typically, one diode will fail with age and vibration and the opposite coil will stop firing.
A good test for checking if both cylinders are working and producing power is to use a spray bottle and spray water on each exhaust pipe. The water should burn off of each pipe quickly if each side is working correctly.
If one side is still not working, you likely need a coil.
I recommend Greentree.com or Jack's small engine for any parts you need. Avoid Amazon, too much junk and defect parts there. You will need the engine label model numbers.
