Blot the spilled nail polish remover with paper towels as quickly as possible. Do not rub or smear the chemical, which only spreads the damage.
Apply the tip of a stain touch-up pen to the damaged desk surface and cover the damage in the direction of the wood grain. Use the pen to draw literally on the desk surface, applying the stain. Add a second coat, if necessary, when the stain dries.
Sand larger areas of acetone damage with fine-grit sandpaper. This helps the new stain blend around the edges of the existing finish.
Shake the can of matching wood stain vigorously to mix.
Apply the stain with a paintbrush in even strokes, moving in the direction of the wood grain. Let dry and apply a second coat if necessary.