The deleteItemAt method deletes an item in a combo box or a list box.
deleteItemAt(System.Int32 nIdx);
nIdx
[Optional] Index of the item to delete. First item is zero. If it is not specified, it will select the current item.
Member of field.
var obj = this.getField("acSelection1");
obj.deleteItemAt();
obj.currentValueIndices = 0;