How to add 2 curves in ARTA

I want to make a near-field measurement, to make a frequency response curve for bass (up to 100 Hz), using ARTA software. I make 2 separate measurements : 1 for the port and 1 for the bass driver. I adjust the magnitude of the port response accordingly (since it has a different diameter than the speaker).

Now I have to add the 2 curves into a single frequency response curve. How do I do that ? I see that I have an average option. But I don't need an average function, I need to directly sum them up.

Can someone show me how ?