Basic Elmers glue is just PVA (most glues are a version of this simply with different amounts of water added). So by soaking it in water, it will eventually dissolve. The problem is #1 you have heat set it with the iron so it could take quite awhile to soften and dissolve. But #2 is what is the added element to make it 'extra strong'. Check the ingredients label and you should be able to google that ingredient and it will have info on removing it. Please let us know what you find out, I'm sure it will be helpful to many of us. Good luck.