What do you do if your lawnmower has no spark?

you replace the spark plug

If after replacing the spark plug you still have no spark you may want to check depending on year and model of lawnmower:

- wire to kill switch might be shorted.

-Take flywheel cover off and clean dirt and rust off flywheel and coil

-if it has points and condenser you will have to pull the fly wheel and replace them and reset points then put back together.