What is the step button on a grand Cherokee to reset service engine soon light?

There is no single "step button" on a Grand Cherokee (or any other car) to reset the "Service Engine Soon" light. That light indicates a problem detected by the vehicle's onboard diagnostic system (OBD). You need to address the underlying problem, not just reset the light.

The light can be reset using an OBD-II scanner, either a professional-grade one at a mechanic's shop or a less expensive handheld device you can buy. Even some smartphone apps, paired with a Bluetooth OBD-II adapter, can read and clear trouble codes.

Simply resetting the light without fixing the problem will cause it to come back on. It's crucial to diagnose the issue using the scanner to read the trouble codes, then repair the problem before resetting the light.