Now get out the pen tool. You just need to draw / drag out three points. It might help to zoom in first. Follow the diagram. This is going to make an outline for your specular highlight.

Click on the first point you drew to close the path.

Your path needs to change into a selection, so click the “Paths” tab. (It should be next to your layers tab). Click on the dotted circle at the bottom of the paths window. Poof! Invert the selection with the select menu (SELECT > INVERSE).

Now cut your new inverted selection (CTRL + X)

Cool, but it looks more like a yin-yang than a button. We need to make some adjustments.

Get the lasso tool and make a selection that cuts through the middle of the circle. Doesn’t matter if it’s not very straight. Feather the selection (SELECT > FEATHER) 5 to 10 px depending on the size of your circle,
and cut. (CTRL + X)