2001 Saturn SL2 Reseting the computer

2001 Saturn SL2 126000 miles

I had my oil changed on Tuesday October 12th, then on October 13 took the vehicle in for an emmission test. It did not pass--no codes are coming up.

How do I reset the computer so I can get me emmission testing done. I have driven it over 200 miles and still the "readiness status" is not ready.

Is there a trick to resetting the computer?

Thanks,

Cheryl