it really depends on the size of the spot, plus your internal state of toxemia, as to the length of fast required to eradicate it.
7 days might not be sufficient time, so I would not set an arbitrary number of days to achieve that goal.
I would also take each day as it comes to observe developments, to rid yourself of this skin condition.
"The exquisite texture and delicate pink color of the skin that develop while fasting attests the rejuvenation the skin undergoes. The clearing up of blotches and blemishes with, even the disappearance of finer lines in the skin, are particularly significant as showing the benefits the skin derives from a period of physiological rest.
That the circulation of the skin is much improved by a period of physiological rest is demonstrated by the way that the blood thoroughly and instantaneously responds to a pinch of the skin. This true "pink of condition" is invariably observed toward the end of the fast and indicates the greatly improved condition of the body. This is to say, the improvement in the skin mirrors the improvement that has taken place within."