AIn this menu you will be able to activate the "Eraser" by clicking Image Added. You can drag the eraser around with your mouse, it will move on the plan dictated by the view. You can choose between a "Cubic" or "Spherical" shape, and then decide on the "Size" and "Opacity".
The "Size" will be the radius of "Spherical" and the length for "Cubic".
Press"D" to erase and "R" to restore