I recently remodeled my house including installing hardwood floors that come prefinished. While applying polyurethane to some trim I dripped some on the floor and did not realize it until it had dried. How do I repair this mishap and return my floors to the was they were?
The only way to dissolve the dried polyurethane is with strong solvents. This would also remove the finish from your pre-finished floor.
One possibility is to use fingernail polish remover, acetone, to soften the polyurethane and gently scrape it up with a plastic putty knife, to reduce the scratches. If a scratch kit is available from the flooring manufacture you could use it to reapply a finish to this area. You could also try a wood finish restorer like <a href="http://www.painters-toys.com/clear-wood-finishes/wood-finish-restorers.html" target="_blank">Howard's Restor-A-Finish</a> of the same or similar color.
Try this first in an area that is normally hidden with furniture.