Copy a row, check table for duplicate, give option to overwrite duplicate before pasting

Hi
I have a workbook (MASTER) that copies a single row of information on contact names and addresses from other workbooks (Slave1, Slave2, etc) and pastes the information into a worksheet (ALL DATA) in MASTER.

Before pasting into MASTER, I want the process to check if the contact information is already in ALLDATA / MASTER. If it is, I need the option of overwriting the existing data, (there may be a change to address or some such), whatever row it's in, or paste the information into a new line if it's a new contact and doesn't cause a duplicate.

So far I've found a process that identifies a duplicate in a single cell in a column, but then asks for you to type in new information to overwrite the information to be pasted, rather than paste over the existing information.

   Private Sub Worksheet_Change(ByVal Target As Range)
'Check for duplicates in the table

        Dim Msg2 As String, Ans2 As Variant
            Dim FindRowNumber As Long
                Dim rng As Range, r As Range, Msg1 As String, x As Range, temp, check
    Set rng = Intersect(Columns(1), Target)
    If Not rng Is Nothing Then
        Application.EnableEvents = False
        For Each r In rng
            If Not IsEmpty(r.Value) Then
                If Application.CountIf(Columns(1), r.Value) > 1 Then
                      Msg1 = Msg1 & r.Value
                    If x Is Nothing Then
                        r.Activate
                        Set x = r
                    Else
                        Set x = Union(x, r)
                    End If
                End If
            End If
        Next
        If Len(Msg1) Then
        
            MsgBox "An Entry already exists for " & Msg1
            x.Select
            For Each r In x
                r.Activate
                Do
                   Msg2 = "Would you like to Overwrite the current entry for " & _
                    r.Value
                    Ans = MsgBox(Msg2, vbYesNo)

 'NEED TO PASTE OVER THE CURRENT ENTRY HERE.........                   
                 
temp = Application.InputBox(Msg2 & _
                    r.Value, "Invalid ; " & IIf(Len(temp), temp, r.Value))
                   check = Application.CountIf(Columns(1), temp)
                   
                Loop Until (check = 0) * (temp <> "") * (temp <> False)
                r.Value = temp
                temp = ""
            Next
        End If
        Set rng = Nothing
        Set x = Nothing
        Application.EnableEvents = True
    End If
End Sub

I've attached a mock workbook in which I copy the list on sheet 2 into column A on sheet 1 to show the above code working, but now need to expand the code to identify the row the duplicate info is in and overwrite it with the info to be pasted, or paste the incoming info as a new line at the end of the list.

Thanks in advance!!

Frankie