How to remove the excess black dye that rubs off from the boots?

You can scrub the shoes with cotton cloth thoroughly and then apply impregnation for genuine leather (available in every shoe shop). Please let the impregnation dry for a couple of hours and then apply it for the second time. After the second impregnation has dried , you can shine the boots with a soft brush. Please inquire about this issue in the shop to make sure you are buying the right agent.