Undo Brush
The Undo Brush tool allows you to reverse the effect of your last action. The Undo Brush acts like an eraser, removing the colour from the previous action.
To use this tool...
Click on the Undo Brush button and point the cursor where you want to start removing the previous action. Move the mouse to begin erasing. The size, opacity and style of the Undo Brush can be changed by double-clicking on the Undo Brush button.