Duplicate Check On Export Of Records

I have a spreadsheet that will export records when I "click" a button, to a spreadsheet on a network drive.

I would like to attach some code that will check to see if a duplicate record is going to be written to the network drive, and if so, alert the user that they are about to create a duplicate . If it is a duplicate, give the user the option to overwrite the existing record.

Ex. I export the results for account 12345.....Account 12345 is now written to an outside sheet.

User2 logs in and works with customer 12345, w/out knowing that someone has already worked with this account, presses the export button.....This is the trigger point for what I want to happen. At this point when it locates a dupe in the outside spreadsheet it will prompt the user too make some chouces .

find attached the code I would like to attach this to...

HTML
option Explicit

Sub TransferData(Optional Dummy As Long)

Dim Row As Long
Dim TargetRow As Long
Dim Path As String
Dim Prompt As String
Dim Title As String
Dim Cel As Range
Dim Wkb As Workbook

Application.DisplayAlerts = False
Application.EnableEvents = False
Application.ScreenUpdating = False

Set Cel = wsCustomers.Range("C:C").Find(What:=Range("C4").Value, LookIn:=xlValues, LookAt:=xlWhole, MatchCase:=True)
If Cel Is Nothing Then
Prompt = "There is no match for the Customer Number (" & Range("C4").Value & ")."
Title = "Process Aborted"
MsgBox Prompt, vbCritical, Title
GoTo ExitSub:
End If
Row = Cel.Row

Set Cel = wsSetup.Range("A:A").Find(What:=wsCustomers.Range("A" & Row).Value, LookIn:=xlValues, LookAt:=xlWhole, MatchCase:=True)
If Cel Is Nothing Then
Prompt = "There is no Workbook Path setup for this Region (" & wsCustomers.Range("A" & Row).Value & ")."
Title = "Process Aborted"
MsgBox Prompt, vbCritical, Title
GoTo ExitSub:
End If
Path = wsSetup.Range("B" & Cel.Row).Value

If Trim(Path) = "" Then
Prompt = "There is no Workbook Path setup for this Customer Number (" & Range("C4").Value & ")."
Title = "Process Aborted"
MsgBox Prompt, vbCritical, Title
GoTo ExitSub:
End If

On Error Resume Next
Set Wkb = Workbooks.Open(Filename:=Path, UpdateLinks:=False)
On Error GoTo 0
If Wkb Is Nothing Then
Prompt = "The workbook for this Customer Number (" & Range("C4").Value & ") could not be opened." & vbNewLine & vbNewLine & "Path: " & Path
Title = "Process Aborted"
MsgBox Prompt, vbCritical, Title
GoTo ExitSub:
End If