Take the Railjet from Salzburg Hbf (or Vienna Hbf) to Amstetten NÖ Bahnhof (RJ 649). From there take the regional train (CJX5) to Pöchlarn and then take the regional train R57 to Wieselburg/Erlauf Bahnhof.
Take the train to Ybbs/Donau Bahnhof. Then take bus number 5 to Wieselburg/Erlauf Bahnhof
Just program the exact data into the online navigation system. You'll get a detailed direction, which you can download.