The other reply nailed it. There is a sort of calcium "hack" your body has for binding to the iron. Try IP-6, colostrum or milk/dairy. At some point your body just stops being able to do it, though. IP-6 to me seems to work even past that point.

Past that, mitigating absorption with green tea seems to help a bunch. And avoiding breakfast cereals. And boxed pasta. I haven't tried turmeric. Despite hearing good things, it seems difficult to source. Everything else pales in comparison to phlebotomy. Of course, you can't donate if you've got on/off fevers.

Also there's some relationship between vitamin D and iron. I'm not clear enough on that to recommend it just for iron, but I will say I do supplement with it, especially through the darker parts of the year.

If you want to drop your ferritin levels, lower your iron (if that is safe for you). The body has no way of dropping iron levels apart from chelation. So, drinking/eating foods that act as natural chelators (ie. black tea) will help. Or, if you're feeling particularly generous, give blood.

(not a doctor, just someone who has hemochromatosis.)