This is a steel frame, with an impact dent in one of the least consequential places possible. The very best course of action is to ignore it and get on with your life. Any attempt to fix it won't change it mechanically except possibly for the worse, and will do nothing other than cost you dough.

OTOH if it really bothers you, consider using body filler and a decal to hide it, and soon enough it'll be out of sight---out of mind.

Edit -- in the intervening time, I lost track. It's an aluminum frame, not steel, but the rest of my answer still holds. Except for the possible negative consequences of trying to fix it. Those will be worse with aluminum vs. steel.

So, either turn it in for a discount on a new bike, or ride it until it dies or you decide to replace it anyway whichever comes first.