"Bevel (Inner)" adds thickness, highlights, and shadows to a picture to create a three-dimensional image. For example this is useful when you want to draw a can badge or a button for a game screen.
Tap ②Filter from the ①Tool Selection window.
Tap ①Bevel (Inner) and adjust the position of the ②Light Source. Set the Height, Smoothness and Highlight Size as you like. When finished, tap ③✓button.
And you're finished.