There is no reset button or procedure for the Check Engine light. The CE light is reset with an OBD2 scan tool. If the gas cap was just loose, then just tighten it, (3 clicks), and after you drive for a few driving cycles the CE light should go off. If it does not then the loose gas cap may not be the problem. This will require the ECU to be scanned with an OBD2 scan tool.