Eczema/dermatitis is a Mars type of disease, being hot, dry, flaky and inflammatory. Mercury or Venus energy works best here.
Saturn rules the protective purpose and structure of skin (thus, put basically, skin in general), while Mercury rules over its ability to move, expand, contract (which eczema can interfere with), and Venus rules over the highest layer, the cosmetic, what others can see, etc.
Either way you want to direct healing energy to the area, to the Middle Chakra and to the opened hand Chakras which are extensions of it, as well as cleansing the effected part regularly.
At very advanced levels one would best use Saturn energy to build the skin and its layers up from something disastrous like a severe burn, not for surface level purposes. In the same way one would harness Saturn's energies to build a structure that lasts forever, not so much the embellishments to the house.