I cannot understand why there are so many views of these questions, with no replies.
I have never seen tutorial. The method below, however, while tedious, is always completely accurate and is quite satisfactory for careful viewing.
I suggest using clone tool in Photoshop, cloning from as close as possible to flaw; in case of sky, be very careful not to have cloning point any higher or lower than flaw. Any remaining evidence of flaw can often be airbrushed over, using a rather transparent setting for brush so that you can add very slowly until the area is exact match for surrounding areas.
