I would be inclined to file 1040X, but assuming your original return was correct except for neglecting to fill out the QDIV line, then all entries would be the same as original, so col A(original) and col C(corrected) would be the same with col B (change) =0.
In Pt III,you can explain what happened (a simple omission) and that nothing really changed.
I do not understand why you do not know if IRS has made an adjustment or not. Are they asking for more money? Can you get their result by making QDIV =0?