It can develop into a very serious condition.
You should go on a pretty much iodine free diet which well help some. You can get iodine free salt and use all you want just avoid most processed foods and eat pretty clean.
Drug treatment (carbimazole), or radioactive iodine treatment, or surgery and possibly all three for the control of the disease.
RAI32
Radioactive iodine kills off thyroid tissue reducing activity of the gland, as well as surgical removal will do so on a larger scale.
RAI is pretty safe as the thyroid tissue is the only tissue in the body that is recptive to iodine that is attached to a radioactive isotope and completely and freely eliminated from the body.
Good luck and start with the low iodine, but keep an eye on the condition because if it worsens it causes heart damage etc.