It is not possible to amend a Supersaver ticket.
You must buy another regular Point-to-point half fare ticket (not Supersaver ticket!) Zermatt-Visp for CHF 18.50. It is then valid together with your wrongly purchased Supersaver ticket (show both tickets upon ticket check).
There is no need to rectify the birth year, simply make sure the date of birth is correct when buying the regular half Fare ticket.