You'll need: sandpaper, white spirits, coloured wood filler, masking tape and a little varnish or floor wax
Frame the burn mark with thick masking tape or two layers of normal masking tape so that only the burn mark is exposed. Use the sandpaper to remove the burn stain, the masking tape protects the area surrounding the burn. Wash the spot with white spirits, then fill in the area with wood filler, let it dry. Using a little wax and a dry cloth rub it 2/3 layers of floor wax. Remove the masking tape. It will not be perfect but will look more like a knot or change in wood colour rather than an ugly burn mark. The success of the repair depends largely on how close to the original floor colour the wood filler is (in my last apartment I added a little white paint to wood filler to lighten the tone). Hope this helps.
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