Userform Verification

I would like to add a piece of code into the user form that will check and verify if a part has already been added so as to avoid multiples in a user-driven/created database.

here is a repost of the current code i am using for the user form (I have posted it before in another thread .. Blane245 helped me out with a different question I had)

Private Sub cmdAdd_Click()
Dim iRow As Long
Dim ws As Worksheet
Set ws = Worksheets("Part_Center")

'the second worksheet
Dim ws2 As Worksheet
Set ws2 = Worksheets(Me.cmbSheet.Value)


'find  first empty row in database
iRow = ws.Cells(Rows.Count, 1) _
  .End(xlUp).Offset(1, 0).Row
  
'check for a Part Number
If Trim(Me.txtModel.Value) = "" Then
  Me.txtModel.SetFocus
  MsgBox "Please enter a Model Number, Part Number or Name"
  Exit Sub
End If

'check for Promo Pricing
If Trim(Me.txtPromo.Value) = "" Then
  Me.txtPromo.SetFocus
  MsgBox "Please enter the Promo Pricing"
  Exit Sub
End If

'check for Standard Pricing
If Trim(Me.txtStandard.Value) = "" Then
  Me.txtStandard.SetFocus
  MsgBox "Please enter the Standard Pricing"
  Exit Sub
End If

'check for Install Required Time
If Trim(Me.txtInstall.Value) = "" Then
  Me.txtInstall.SetFocus
  MsgBox "Please enter the required Install Time"
  Exit Sub
End If

'copy the data to the database
ws.Cells(iRow, 1).Value = Me.txtModel.Value
ws.Cells(iRow, 2).Value = Me.txtBrief.Value
ws.Cells(iRow, 3).Value = Me.txtDesc.Value
ws.Cells(iRow, 4).Value = Me.txtPromo.Value
ws.Cells(iRow, 5).Value = Me.txtStandard.Value
ws.Cells(iRow, 6).Value = Me.txtInstall.Value
ws.Cells(iRow, 7).Value = Me.txtManuf.Value
ws.Cells(iRow, 8).Value = Application.UserName
ws.Cells(iRow, 9).Value = Date

'do the same for the other worksheet
'find  first empty row in database
iRow = ws2.Cells(Rows.Count, 1) _
  .End(xlUp).Offset(1, 0).Row

'copy the data to the database
ws2.Cells(iRow, 1).Value = Me.txtModel.Value
ws2.Cells(iRow, 2).Value = Me.txtDesc.Value
ws2.Cells(iRow, 4).Value = Me.txtPromo.Value
ws2.Cells(iRow, 3).Value = Me.txtStandard.Value
ws2.Cells(iRow, 5).Value = Me.txtInstall.Value
ws2.Cells(iRow, 6).Value = Me.txtManuf.Value


'clear the data
Me.txtModel.Value = ""
Me.txtBrief.Value = ""
Me.txtDesc.Value = ""
Me.txtPromo.Value = ""
Me.txtStandard.Value = ""
Me.txtInstall.Value = ""
Me.txtManuf.Value = ""
Me.txtModel.SetFocus
End Sub