Dear Shawn
This is especially difficult repair to do. The hot iron approach is valid but you will have to remove the finish first. You can do this by sanding the area, or applying a chemical stripper to expose the bare wood. Just the corner of the rag wetted will do, as you apply the hot iron. Use distilled water so you don't cause a mineral stain if your water has iron in it.
You can also try drops of rubbing alcohol and the tip of a hot new clean soldering iron. Rubbing alcohol contains enough water to puff out the dent (on bare wood) without damaging the finish too much.
But now you have to touch up the finish, and most likely re-coat the entire floor. Be sure to wait until the spot has dried overnight before you touch-up. And know your floor finish. Most floor finishes will not blend in well, and you will have to re-coat the whole floor, and even then it will not perfect. I know, because I have to do such repairs for insurance companies, and even I have a hard time making the repair invisible.
But it can be done. Sand well between all coats, and allow each coat to dry 1-2 days. I'm talking about the touch-up coats. Once the area is filled in with at least 2-3 coats of finish, let this cure for about a week, and sand level, with 120 grit sandpaper, then re-coat the whole floor.
You might consider puffing out the dent, and having the whole floor re-sanded, instead. It's called hardwood, but it's still wood, be careful with heavy objects.
