To move the front-sight base, knock it slightly with a hammer or use a special attachment.
Knocking it slightly will not work.
After soaking the sight overnight in CLP or some other good quality penetrating oil, get a punch with a broad base, a good hammer, and a friend who has a vise (if you don't).
Open the jaws of the vise just enough to permit the movement of the FSB cylinder. Lay the barrel over the vise with the cylinder centered on the open vice jaws. Have the friend hold the rifle securely in place. Center the punch on the cylinder and strike the punch very hard at least twice. Check to see if the cylinder moved. If not, continue the process until you see movement. Once the cylinder moves, soak it again with CLP, and then use the front sight tool to actually do the sighting in.
BTW, this is a good site to read to learn about how to sight in an AK: