Reduce [CO], reduce the pressure and raise the temperature.
Le Chatelier's principle tells us that any change imposed on the system causes it to shift in a manner that counteracts the imposed change.
From what we know about this reaction, to get a shift to the left (reactants) we could
- reduce the [CO]. This will cause the reaction to shift so as to replace the "missing" CO
- reduce the pressure. Since the reactants contain a greater quantity of gas (three moles to two), a reduction of pressure causes a shift to the left to increase the amount of gas, and raise the pressure back up.
- raise the temperature. Since the reaction is exothermic, it gives off heat as it moves to the right. So, the reverse reaction is endothermic. If we raise the temperature, the equilibrium shifts in the endothermic direction (tot he left) to absorb heat and bring the temperature down again.