How do you fix high HC CO and NOX readings?

I guess your cat/s needs to be changed. Co is high due to a rich A/F mixturewhich is a compensation for a lean running conditions. Like a vacuum leak, bad o2 sensor, or a bad cat that will trigger the engine light on. High nox is due to a hot running conditions because of lean or rich air fuel ratio, bad thermostat, and sometimes bad coolant temp sensor.

Many things to look at, just make sure before you swap anypart that you have a code that will help point you in the right direction