You can try these instructions for removing iron on rhinestones on a fabric. As written on www.crystalsrus.com
1, Test a small, non-visible area of the fabric to ensure that the acetone or acetone nail polish remover will not stain or otherwise damage the material. Dab a cotton ball soaked with acetone onto the fabric and allow the fabric to sit for a few minutes. Rinse the area with water when the test is complete.
2, Dampen a cotton ball with acetone or nail polish remover and dab the cotton ball onto the glue.
3, Blot the affected area with a clean cloth. The acetone will break down the glue, which the cloth will pick up. Continue applying acetone and blotting with the cloth until all of the glue is removed.
Cold Water Method
4, Place the piece of clothing with the iron-on glue into the freezer. Leave the garment inside until the glue becomes cold and brittle.
5, Remove the item from the freezer and quickly get to work scraping off the glue with either a dull knife or a spoon.
6, Continue scraping until all of the glue is removed. Because the glue is frozen, it should pop off easily.
7, Place a piece of cotton fabric flat onto an ironing board. Place the fabric with glue residue glue-side down on top of the cotton fabric.
8, Apply a hot iron, but do not use the steam function, to the item for 10 to 20 seconds. This will bind the cotton fabric to the glue. Remove the iron and peel the fabric from the iron-on. When you peel the fabric away, the glue will come away as well.
9, Repeat until all of the glue has been transferred to the cotton fabric.
Hope the above methods will help you remove unwanted rhinestone transfer designs completely someday. In most cases, they will function well. You are also welcomed to share your ideas to remove iron on glue.
Hope this helps.