How do I reset the ''service'' light on 98' Infiniti QX4

Hook a generic scan tool to the white plug under the dash & record on paper the code u also looked & wrote down the freeze frame data then clear the code. P0420 codes for the cat converters r common to that year. Other notable codes P0455 gross evap leak, caused by loose gas cap. Once the code is cleared the car needs to be driven from cold motor for about 20 minutes to do all the diagnostic things to pass emission tests. The engine light wo not return until the computer sees the same failure two times. Gray plug at the fuse box is for Nissan techs like me to use.