Any file that fits the notch will work. One that is square on the corners and preferably one not too course. I suspect the sight is relatively soft so material should come off pretty easy. An ignition file (some are rounded so won't work) or a small file with cutters on the edge. Usually one side cuts, the other is a safe or smooth edge.
Bearing in mind that you don't want to over do. You can take more off but you can't put it back. Been there a time or two.
In Memory of Paul "Dietrich" Stines.
Dad: Say something nice to your cousin Shirley
Dietrich: For a fat girl you sure don't sweat much.
Cue sound of Head slap.
RIP Muggsy & TMan
"If you are a warrior legally authorized to carry a weapon and you step outside without that weapon, then you become a sheep, pretending that JOCKO will not come today."