How do i re-set the service warning light on my 2003 Alero?

If you talking about check engine light. or service engine light. you have to use a code scanner.to turn off light.but if the light coming on while driving . you got a bad sensor . the light will stay on until you fix it. if you got a code scanner it will tell you what sensor is bad .it will give you a code.

This depends on which light you are reffering to. There is a sercive engine soon light, and a service vehicle soon light, as well as other warnig lights.