Hello,
the chin area is difficult. There is strongest beard I think and shape is convex. So you can not apply pressure at all.

Just go slow with no hurry. Remember to stretch your skin, it helps to cut the beard. And propably if you have some very hard spot like often are under jaws, you can move it to other position by lifting your cheek. Hope you got the point.

The beginning is always hardest. Good luck.