There’s a couple of ways you can do it. Some people lay the hook in where they want and take a mallet, something besides steel, and hit the mold to leave an imprint. Then take a dremel and go to work on the mold. Relieve both sides so it’s symmetrical.
Another way is to clean the face off with acetone or other solvent, lay the hook where you want it, and spray some Frankfort release over it and that will leave an outline to work from. I’ve done it both ways.
With all that said, I prefer using the flat and ball end mills in my drill press with a drill press vice for these jobs as opposed to the dremel. Much more control as the dremel always wanted to run away when I tried with it.