Question

how could you increase the potential energy of the apple?

Answer 1

By putting an apple up on high ground. (That is 1 example)
This creates a higher gravitational force, and when it falls down it would have a lot of kinetic energy. But, if put on low ground, it wouldn't have enough potential energy to increase the kinetic energy.

Answer 2

You can increase the gravitational potential energy of an apple
by gluing it back onto the tree-branch that it fell from.

Actually, by just lifting it to any place higher than where you find it.