Chappal tan on feet is because the tanned area is not covered by your footware. So make sure that the feet are fully covered with your footware. So not rub the affected area in attempt to remove the pigmentation. Similary cover your hands while outside especially while driving. Alternatively you can apply any good sun screen with SPF 50 while you are outside.
Next Steps
you can take chemical peeling sessions to fade the tanning faster along with creams containing glycolic acid.
Health Tips
fully cover the affected area and protect it with sunlight will help to avoid such tanning in future.