You don't add more yeast- once it's fermented, there aren't any more sugars for them to eat. Now you let it sit, clear up, and condition a bit. In a few weeks, there will be some lees on the bottom of the container that have some dead yeast and other things in the bottom. When that gets about 1/4 " thick, you rack again and top up with water (or a similar wine) to the top. And wait some more.
Wine making requires a bit of patience, so just throw a towel over the carboy and walk away for at least a month.