Exactly so... In short, set the "Notch" or Gain to a negative number down from the detent center position. Set up the feedback as described above, then sweep the frequncy knob back and forth until the feedback starts to fade. At that point you are trying to localize the exact frequency that is feeding back, then adding or subtracting the Notch or gain at that frequency to reduce the feedback.

Be advised you may have more than one frequency that is prone to feedback, due to harmonics or room frequency or number of people in the room, temperature, humidity, or windage (no I'm not kidding). The best thing to do is to catch the earliest feedback with the notch, then use the amps EQ to try and catch the others as they become apparent. You need only do this up to the point where your overall volumn is sufficient to play out your gig. Unless your amp is in the one location in the world you must have it to play your gig, consider moving it as well (they always sound better up off the ground anyway - which is the reason they make amp stands - but two chairs placed together will do as well). Good luck!