“Boomy” bass almost always traces back to one or two narrow peaks in your measured response, usually somewhere between 40 and 120Hz, caused by your room's dimensions reinforcing those specific frequencies (a room mode).
Start by identifying the peak's exact frequency and height on your RTA sweep. A parametric EQ filter set to that frequency, with a moderate Q (bandwidth) and just enough negative gain to bring the peak down to the surrounding curve, is usually the most effective fix — resist the temptation to also cut everything around it.
If the peak is severe (more than 8–10dB), consider physical changes first: moving the subwoofer away from corners, or moving your listening position slightly, can reduce a room mode's severity before you reach for EQ at all.
Always re-measure after applying a fix. A correctly tuned filter should flatten the peak on your RTA sweep, not just change how it sounds — if the measurement doesn't confirm the fix, the filter is probably set to the wrong frequency or Q.