SDK change mode form into update

Hi

my code add a matrix

form.DataSources.DataTables.Item("oMatrixDT").Clear();

string sSQL = "Select U_VisOrder,Code,U_LabelNr,U_ObjType,U_DocNum,U_DocEntry,U_Series,U_ItemCode,U_ItemDesc,U_DistNumber,U_UnitMsr,U_Qty,U_PackNr,U_PackQty from [dbo].[@SSAINFO_PRNTLBL] T0 where U_ObjType=15 and U_DocNum='" + sDocNum + "' and U_Series=" + sSeries + " order by U_VisOrder,U_LabelNr";

form.DataSources.DataTables.Item("oMatrixDT").ExecuteQuery(sSQL);

if I add records to show into matrix a see new data correctly into matrix but form doesn't show "Update" button

can I force something to change mode form? thanks