tisp on adjusting fixed rear sight on berretta

[bubbapug1]

I have a Berretta 92fs. I started to practice out to 17 yards and my groups drifted left severly. None of my other guns do so..upon clsoed inspection we discovered teh rear sight is off off center to the left. Any ideas on how to tap that sight back into place? I have tried a wood dowel with a nice size hammer..thought for sure it would move, but after repeated blows (with no marring) it won't budge.