Nail varnish remover is v powerful stuff.
Your options...
Leave it as it is - anything you do will probably look worse than it currently is. Cover stain with a coaster. 9/10
Apply same treatment to whole of the top surface to even out the discolouration. 3/10
Strip off existing and refinish. 7/10
Invest in a replacement unit. 10/10
Richard Buxton, September 2008