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.