Workbench shp to s-57

How can i transfer shp to s-57. The shapefile has attribut "Wasserstnd" with value 1 or 2 or nothing. The result must be slcons with attribute watlev =4 , if Wasserstnd is 1 or slcons with attribute watlev =3, if Wasserstnd is 2 or slcons(not specific value for watlev), if Wasserstnd has not value. How to make the workbench? Thanks!