Drift that puppy!
A 'NON MARRING' punch or drift is the ticket with fixed sights. Brass is best, although a plastic or nylon piece will work in a pinch. I've used (with good results) a square section of brass about 4 inches long with my hammer for a number of years.
Do not use any iron or steel drifts or punches, as they will marr the finish in an instant, and will really tick you off.
You might be surprised at how much 'Omph' you might need to actually move those sights. I actually do the drifting at the range, so I can instantly monitor the results. Just ensure that you have a completely safe and unloaded pistol before you attempt to do this operation!
You will want to be tapping on the right side of the sight (moving the sight to the left). A couple of good taps should get you to where you need to be. Too much 'omph' could possibly drift the sight right out of the dovetail slot. No worries, just replace it and drift her back to where she needs to be.
Good luck, and let us know how you fare.
Unkel Gilbey