I don't believe this is possible without having to repaint the whole dial, you've got paint on paint. I'd be resolved to repaint the whole thing. In any case I'd (first) try to remove the white lettering with "Goof Off."..... Probably won't work. Or you could try to match the original black paint, and mask off the area, and spray over the lettering you want removed. Or forget removing it altogether and apply a black magic marker to the lettering....