It all depends on how much windage adjustment you need to bring it to point-of-aim.
The simplest solution is try various brands of ammunition and bullet weights, and different grips (stocks). Bullet weight will have a big effect on point-of-aim versus point-of-impact, especially with snubnose revolvers. Same thing with the grips.
Since you have already filed on the front sight, a little more filing is not gonna hurt the value of the gun.
You can file the rear sight notch wider...in the SAME direction that you want the groups to go. Or, you can file the front sight thinner.
Remember, you want the front sight to move in the OPPOSITE direction of the way you want the groups to move. In other words, file on the LEFT side to thin the blade if you want the group to move LEFT (thinning the blade on the left in effect moves the blade right).
An alternative to filing on the front sight is to bend the blade, ever so gently. This is only feasible on guns that have enough front sight blade to bend. It won't work for example, on a S&W M60 that has a tiny ramp. Again, bend it in the direction OPPOSITE to the direction you want the groups to go. This can be done by (firmly) supporting the barrel on a 2x4 block and bashing on the front sight blade with a plastic non-marring hammer. Not much movement is needed.
Finally, and this is where a capable gunsmith is required. Simply tightening or loosening the barrel a few degrees (re-index the barrel) is enough to often enough to correct a bad windage error. This would require the proper gunsmithing tools: frame blocks, barrel vise, etc.
