plugas

Hi all When I create an image made up of multiple layers then save it as a JPG, the image must be flattened, but a notification box pops up (see attached image) that states: "The image will be flattened, and then saved. You will be able to undo the flatten operation after saving is finished." But if I go to that JPG file later I simply cannot find how to undo the flattening..!! Any help appreciated!