Get an acidic liquid, such as nail polish remover, vinegar or lemon juice. Pour a small amount, perhaps a tablespoon, into a small disposable paper cup.
Dip the tip of the marker in the liquid. Allow a bit to soak in, but don’t saturate it.
Place its cover over the marker. Turn it tip-side up and place it in a cup or holder.
Let it sit overnight.
Try writing with your marker the next day on scrap paper. If the tip is still very wet and the color is coming out light, recover it and allow it to sit a while longer until the tip is dry.
When the tip is dry, if there is still ink inside, the marker will work. If the marker doesn’t work, the ink is dried out and there will be no way to restore your marker.