=If substr([Material];1;6)="000000" Then replace([Material];"000000";"") else [Material]
or
=If Left([Material];1)="0" Then Substr([Material];7;Length([Material]))
=If substr([Material];1;6)="000000" Then replace([Material];"000000";"") else [Material]
or
=If Left([Material];1)="0" Then Substr([Material];7;Length([Material]))