Try using a walnut on it (the wooden floor installers I've dealt with in the past swear by it):

  https://www.wikihow.com/Seal-Wood-Scratches-With-a-Walnut

  You could try steaming it to lift the dent out (moisten and expand the wood fibres) and then walnut it.

   https://homeguides.sfgate.com/repair-wood-grain-rise-steam-99306.html

Ouch. Bet that ripped your undies. Is there a more hidden spot you can try stuff on? 

You can cover with a thin wet cloth and hold a hot iron to it. That will cause the wood to expand and hopefully pop it out. But it can also cause the finish to lift so you'd want to try carefully.

You can also get wax fillers in a range of colours, and you can blend waxes to match. It won't be a perfect match but could well improve it.

Walnut lol....doesn't work, not that deep anyway.

Sand it and revarnish.

It looks like it's indented rather than scratched. Use a steam iron and a damp cloth, testing on a small area first which is out of the way. Apply the iron over a damp cloth for a few minutes - enough to get the wood steamy and hot to the touch. Then leave it for a few hours before checking again - you might need to repeat it a couple of times. Eventually the wood fibres will swell with the moisture and pop up again. You shouldn't need to re-varnish it, just touch it up with some floor polish.

Don't worry if the surface goes a milky white - this is normal for polyurethane finishes with moisture and will go away after it dries out (which might take a day or two).

Don't sand the floor - you would have to grind it down by about 0.5mm to get those marks out, and most likely would end up needing to sand and re-varnish the whole room to make the area match.

I agree with the steam not sure of the finish on there but with furniture i leave a damp tissue on the dent for a day or trickle water into the dent let it soak for a day then wet cloth and steam iron