[williamting]

If you have "overdone", the easiest is to pull the Master Fade slider left. Failing this, use a big and light (Brush Strength) Restore Brush and gently "sweep" over the affected area.

If you use Touch up brush, do experiment with different brush strength. Strong brush may give you unwanted effect.

If you have saved the picture already, you cannot undo.

I hope the above helps.