How do you get the interior 'system check' light to turn off on a 1990 Acura Legend?

usually when the check engine light comes on it is most likely to be a o2 sensor i had a 1990 legend and i had the light turned off and it came back on 5 minutes later the mechanic said it was an o2 sensor wasn't cheap to replace the part cost about 80 bucks and they charged me 75 to install because there is tool you need to twist off the sensor