You have to determine if the wood is missing form the gouge, in this case you can deepen it with a nail punch, and fill with a light colored epoxy putty. Let the putty cure, sand flush, and stain and color the grain until it is blended in with the wood. then touch up the floor finish.
But if the wood is merely compressed, you will have to remove the finish from that spot, by chemical stripping or sanding to the bare wood. Then use a hot clothes iron and a clean white rag wetted on a corner, and steam puff the dent back to the surface. Wait overnight for it to dry, and touch up the finish. Read my article in the Floored News section about floor maintenance, both parts, to determine your floor finish, and other methods for general maintenance.
This may be all too much trouble, and you might instead just enjoy the character marks your wood floor is gaining as it ages, just like us humans.
As always your Most humble servant, Joseph, the Wood Floor Doctor.
You may also find these articles helpful:
1. How To Repair A Hardwood Floor For D.I.Y
2. Orbital Floor Sander
3. Should I sand the wood floors myself or hire a pro
4. Plank Floor: What Special Considerations This Type Of Floor Raises
5. How To Take Care Of Your Health And Safety when Installing, Finishing, Repairing or Cleaning your wood floors