How can I reset the master warning light

 

Turn off the vehicle, no IGN, no ACC, no nothing. pump the brakes to deplete any power in the system, then pop the hood and disconnect the negative(black) battery terminal. Wait about a minute or so, then put the lug back on the terminal and put the cover on, then try starting the car. Warning light should be gone.

On a second note, if you suspect that the warning light is on for a reason, you should probably have that reason investigated. It would be bad if you turned off a master warning light for a loss of power steering or ABS or something mission critical.