While the simplest answer is to strip the entire figure and then repaint it (if you did the body well once, you can do it again), there are commercial paint-stripping products that will let you strip a portion of a figure as needed (gels and such). You simply dab them on the area and then carefully peel away the paint. It will be a finnicky job though, as you will have to carefully clean the head of stripper before new paint will adhere. Simplest to re-do the whole figure.
If the face is a featureless blob after three coats, it sounds like you're not thinning your paints enough though...