thank you for reply

I have three tables

Patients
Expense Reports
Expense Details

relation ship like this

patients----Expense reports----expense details

one patient may have many expense reports
one expense report may have many expense details

primary keys:
patients=Patientid
Expense reports=ExpenseReportid
Expense details=ExpenseDetailsid

the record source for the main for which "Expense reports by patient" is the
table patients

the record source for the subform which is named as "patients subform " is

like this example( as i am not at office now and dont have the db with me at
home.but this is a simillar sample, same idea , I took it from the sample db
expenses) using the join between  two tables : expense reports and expense
details

SELECT DISTINCTROW [Expense Reports].ExpenseReportID, [Expense
Reports].ExpenseRptName, [Expense Reports].DateSubmitted, [Expense
Reports].AdvanceAmount, Sum([Expense Details].ExpenseItemAmount) AS [Total
Expenses], [Expense Reports].Paid FROM [Expense Reports] LEFT JOIN [Expense
Details] ON [Expense Reports].ExpenseReportID=[Expense
Details].ExpenseReportID WHERE (([Expense Reports].patientID=forms![Expense
Reports by patient]!patientID)) GROUP BY [Expense Reports].ExpenseReportID,
[Expense Reports].ExpenseRptName, [Expense Reports].DateSubmitted, [Expense
Reports].AdvanceAmount, [Expense Reports].Paid;

actully , although i am using access for about two year , but i am not
fimiliar with codes , that why i need some help :

1.how to save the primary key Expenserportid to use it for the next sql
which is for the third table "expense details"

is it like this:
Bookmark = .LastModified

      lngID = !Expensereportid
and where should I put it

2.what i should put here for the slq 2

FROM [Expense reports ] WHERE patientid = " &
Me.PATIENTID & ";"
should it be like this

FROM [Expense details] WHERE Expensereportid= " &
Me.Expensereportid & ";"
or it will not work her because the control expensereportid is not in the
main for , it is in the subform?

i have tried and i reached this stage

Private Sub cmdDupe_Click()
'On Error GoTo Err_Handler
   'Purpose:   Duplicate the main form record and related records in the
subform.
   Dim strSql As String    'SQL statement.
   Dim strsql2 As String   'for expense details (is this right like this)
   
   Dim lngID As Long       'Primary key value of the new record.
   
   'Save and edits first
   If Me.Dirty Then
       Me.Dirty = False
   End If
   
   'Make sure there is a record to duplicate.
   If Me.newrecord Then
       MsgBox "Select the record to duplicate."
   Else
       'Duplicate the main record: add to form's clone.
       With Me.RecordsetClone
           .AddNew
               !TransactionDate = Date
               !DiagnosisCategoryId = Me.DiagnosisCategoryId
               !Cpr = Me.Cpr
               !CountryId = Me.CountryId
               !AuthorityId = Me.AuthorityId
               !PatientNameId = Me.Patient
               !Gender = Me.Gender
               !CaseCategory = Me.CaseCategory
               'Enter all the fields required
           .Update
           
           'Save the primary key value, to use as the foreign key for the
related records.
           .Bookmark = .LastModified
           lngID = !PatientId
           'Duplicate the related records: append query.
           If Me.[patients Subform].Form.RecordsetClone.RecordCount > 0 Then
               strSql = " INSERT INTO [Expense Reports] ( BatchId,
BatchNumber, BatchDate, DocumentType, Cpv, CpvDate, EntryReferenceId,
EntryReferenceAmount, ROE, FcAmountXR, [Currency], TransactionDate,
LastUpdateby, ChqNo, PostingRestriction )" & _
                   "SELECT " & lngID & " As NewID, BatchNumber, BatchDate,
DocumentType, Cpv, CpvDate, EntryReferenceId, EntryReferenceAmount, ROE,
FcAmountXR, [Currency], TransactionDate, LastUpdateby, ChqNo,
PostingRestriction " & _
                   "FROM [Expense Reports] WHERE patientid = " &
Me.patientid & ";"

'not sure about it
strSql2 = "INSERT INTO [Expense Details] ( ExpenseReportID,
ExpenseCategoryId, InvoiceIssuerCategoryId, ExpenseDescriptionId,
ExpenseItemDetails, AccountingDate, InvoiceIssuerId, TransactionDate, Period,
AdvancePayment, PostedExpenseDetails, Deductions, Rejected, Discounts,
InvCat, InvPart, ExpenseItemAmount ) " & _
                   "SELECT " & lngID & " As NewID, ExpenseCategoryId,
InvoiceIssuerCategoryId, ExpenseDescriptionId, ExpenseItemDetails,
AccountingDate, InvoiceIssuerId, TransactionDate, Period, AdvancePayment,
PostedExpenseDetails, Deductions, Rejected, Discounts, InvCat, InvPart,
ExpenseItemAmount " & _
                   "FROM [Expense Details] WHERE Expensereportid = " &
Me.Expensereportid & ";"

               DBEngine(0)(0).Execute strSql, dbFailOnError
           Else
               MsgBox "Main record duplicated, but there were no related
records."
           End If

               DBEngine(0)(0).Execute strSql, dbFailOnError
           
           Else
               MsgBox "Main record duplicated, but there were no related
records."
           End If

           
           
           'Display the new duplicate.
           Me.Bookmark = .LastModified
       End With
   End If

Exit_Handler:
   Exit Sub

Err_Handler:
   MsgBox "Error " & Err.Number & " - " & Err.Description, , "cmdDupe_Click"
   Resume Exit_Handler
End Sub