Chlorine dioxide is too unstable to last for any length of time in a skin cream. You can use sodium chlorite. If the eczema is caused by a fungus the sodium chlorite should clear it up.
You can take a normal skin cream and add enough sodium chlorite to achieve a concentration of 50 PPM. As a reference, 1 ml of Miracle-Mineral-Supplement has a concentration of 240000 PPM in 1 liter of water.