One generally needs a wide band to adjust it to exactly 14.7. Unlikely to find one easily other than tuners.
A gas analyzer will get you close but not exact based on CO and CO2 emissions.
On the other hand, using a scan tool can help to give access to a 'certain' Manufacturer Specific PID that tells if the mixture is set lean or rich. Then again, one needs to know at what value that parameter is factory set to.
No, I am not talking about Lamda or Fuel Trims. Those only show up in LIVE DATA when the vehicle is equipped with an O2 sensor
Like @xulfiqar bhai said, only change if you know what you are doing. A rich wont cause that severe a damage as a lean would.
there's an old saying
IF IT AINT BROKE, DONT FIX IT (not to be applied to preventive maintenance)
