tincture of iodine is a mixture of potassium iodide and iodine in alcohol or water, the best method to add is to dilute the mixture with water and add some kind of oxidizing agent (sodium percabonate may work, but hydrogen peroxide is better not to use iodine is an excellent catalyst for the decomposition of peroxide). So you excrete additional iodine from potassium iodide + iodine.