Heater blows cold air

Blend door or heater control valve? If you are adding antifreeze you have a leak. Once coolant is full, you should never have to add unless you are changing it out. So you have a pressure loss somewhere in your system. Have the system pressure tested

I agree with the above, but with that new of a vehicle, it should still be under warranty, I would take it to a dealership to have it repaired.