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If the protective coating of the hardwood floor is scratched, use a soft rag (such as a microfiber cloth) and a small amount of hardwood floor cleaner to remove any contaminants from the scratched area. Any and all small dust particles must be removed from the scratched area so they don’t get preserved in the floor when you add sealant. After cleaning the scratched area of the floor, dampen another rag with water, and wipe down the scratched area to remove the cleanser. Let the scratched area dry before moving on. When the scratched area is completely dry, use a small tipped brush to apply a thin layer of protective finish to the scratched area of the floor.  This protective finish could be a sealant, shellac, or some other kind of polyurethane varnish. Ideally, you would use the same kind of finish that is already on the hardwood floor.  Consult an employee at your local hardware store for advice on what kind of finish you should use on the floor. If you are an inexperienced wood worker, or if your hardwood floor has a specialty finish (such as a high gloss polyurethane finish), consider hiring a professional to repair and finish the floor.  Since hiring a professional will cost more money, it might be most cost-effective to let scratches accumulate, rather than hiring a company to fix one small scratch.
Clean the scratched area. Rinse off the cleaner. Apply a top coating.