I Have A 2006 Trailblazer And When I Changed The Oil I Left The Oil Cap Off And Rove It About 15 Miles And The Check Engine Light Came On. I Put The Cap Back On Immediately, But The Light Won't Go Off. How Can I Reset The Check Engine Light?

To reset system turn engine off, turn ignition key to run position and press the gas pedal all the way three time in five seconds, the oil life light will blink five times and you system is reset, turn the ignition key to off position and you are done. Good luck.

Could be the sensor is stuck will have to have a tool to reset it .
Sometimes the sensors once have came on then have to be reset before can work properly. This happens is not unusual.