This is used to remove spots from the surface of the lense, artefacts caused , due to dust particles or water droplets, and scratches and dust from old photographs.
Double-click on an image once it is added to an album.' Under the 'Basic fixes' tag, select 'Retouch'. Use the 'Brush size' slider to select a brush size. Ideally, you should select a brush size a little larger than the size of the artefact you are trying to remove. Click once on the blot, and click to a similar place elsewhere in the picture. The smaller the brush size, the less noticeable the patch up will be. Hovering over different parts of the picture, you should see the blot getting covered up. You can undo a bad patch in this window itself. Once you are done fixing everything, click on apply. If you want to undo your changes, you cannot automatically
,redo them.