How do you make it so when you toss an item into soul fire, it converts into another item?

So I'm trying to make it so when you toss an item in Soul Fire, it turns into another item, so item conversion by soul fire!

I'm not quite sure how to do this and any help would be appreciated for this since it's pretty necessary for what I'd like to add into my mod.

The Process is just tossing the item into soul fire, then it converts into a new item from that soul fire, idk.