I think you mean carbon dioxide (CO2, not CO. CO is carbon monoxide). But increased oxygen does not decrease the CO2. You have to ascertain the source of the CO2 and address that
The only connection is that they both are components of air. However, if you burn something containing carbon atoms, it will usually produce carbon dioxide as in the case of bush fires, coal, natural gas. Only photosynthesis takes the carbon dioxide in large quantities out from the air and fixes it as complex organic substances such as glucose, lignin etc.. Hence the importance of vegetation.