As it's hardened do no use heat , Acetone or MEK will soften it enough for you to wipe it off , Nail varnish remover normaly is Acetone with something like Lanolin added , Use that as it is the solvent acting on softening the residual glue so you can wipe it off , wrap it in paper towel's and drizzle the solvent on to the towels and leave for 10 min and then wipe off.