Ok, hold on to your hat for a second.

Iron is naturally occurring in the soil and you don't usually get toxicity issues unless there's a source such as mining, tailings or a junkyard or something like I suppose.

The liming agent depends on what you want to use. Typically it's something with a higher pH such as wood ash (careful), bonemeal, or lime (CaO)

By adding the Liming agent you increase the soil pH and reduce the availability of iron in the soil. The total amount of iron will still be there but it will be in unavailable form