How do you turn off engine light on a 2009 Mercury Marquis

The Check Engine light must be reset using an OBD-II code reader. Dealers have them as do repair shops. Places like AutoZone will read the codes for you, but normally will not reset the Check Engine light due to possible liability issues. You can purchase a code reader at these places to do this yourself. Make sure you get one that can read and reset the engine light. The very cheap ones cannot reset the Check Engine light.