That is the bolt that lets you move the sight up and down. There are set screws in the bottom that will let you twist the sights. “Canted sights” means your sights are twisted, or “canted”, to one side or the other. To adjust that....Use a marker of some sort to draw a line on both the sight base and the barrel, then loosen the set screw, twist the sight base the correct direction, using the line to see how far you are going. Tighten the set screws, re-zero the weapon. Repeat if needed.