It is scab, a fungal disease. Granny Smith is very prone. It will disfigure the outside of the fruit, but if you peel off the, skin the flesh is fine.

Is there I can do?

It is too late now to do anything for this season but you might want to do some research on how to treat going forward. Generally, you will want to do preventative fungicidal spraying when the conditions are right for the disease to proliferate.

Apple Scab Fact Sheet

FWIW, it is not always necessary to treat. It depends on the apple type, how well the tree is established and your tolerance for less than perfect fruit and foliage. I grew a Gravenstein apple tree for years - they are also very prone to scab - but it is my favorite variety. I never sprayed. I would get some leaf drop (heavier in some years than others) but the tree was mature enough and well established enough to tolerate it easily. The fruit was only mildly disfigured and still completely edible. YMMV