If your wine is too acid, this will reduce it.
Taste the wine and run it around your mouth.
If there's sweetness but lots of sourness/acidity then this stuff will help.
Most of the time it's just too dry- that is a sour taste. It tastes sour with no sweetness, if it's like this then you need to add sugar! Also add a campden tablet and stabiliser or it will start fermenting again!