Hi, if it's the purple air erasable ink or the blue water soluble ink, in my experience, when you iron over them, they are set in the fabric. Maybe someone else knows how to get the marks out. A ball point pen mark is made with different chemicals that are soluble in hairspray, but that wouldn't work for these marking pens.
I once made a garment (before quilting
) and ironed over the markings on the cuff. As many times as I washed that garment, the marks were still there
Kathy