Does listerine mouthwash help decalcification?

It may slightly: If may help minimally if it has Fluoride in it. If you have decalcifications, discuss it with your own dentist who can properly advise you what can be done. It depends upon where they are, how big, how deep, if it's an esthetic or a structural concern, etc. Dentist have many methods to help remineralize the enamel or cover\repair the surface destruction of the tooth.

Possibly: You are probably thinking of the difference between antiseptic mouthwashes versus Fluoride mouthwashes. The only mouthwash that can help prevent or re calcify incipient decalcifications are Fluoride mouthwashes. Listerine does make a version of its mouthwash with fluoride. It is called listerine Fluoride defense.