See Phlearn Retouching 201 Section 2, 29:43-39:42.
Use this to even out skin tones . It can even larger areas more smoothly than dodge and burn but can reduce some skin texture, which can be put back with noise. Even more powerful when combined with frequency separation.
Create a new layer and change the blend mode to luminosity. Edit in black and white by having a Black & White adjustment layer active. Paint at a 5-10% flow with black or white.
