Where clause in OleDbCommand in vb.net

I do not understand what I am doing wrong!

Protected Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
    Dim con As New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Users\stagiaire\Desktop\App_Web.MDB")

    Try
        con.Open()
    Catch ex As Exception
        Response.Write("<script language=""javascript"">alert('Pas de Connexion');</script>")

    End Try

    Dim da As New OleDb.OleDbDataAdapter("select * from stats", con)
    Dim ds As New DataSet
    da.Fill(ds)

    Dim aString As String
    Dim num_off As String
    aString = CType(Site1.nom, String)
    num_off = CType(WebForm1.num_of, String)
   
    Dim cmd As OleDbCommand = New OleDbCommand(String.Concat("insert into  [stats]([op_10]) Values (" & 1 & ") WHERE ( [numero_of ]='" & num_off & "' )"), con)
    Dim drlog As OleDbDataReader = cmd.ExecuteReader
    If (drlog.Read() = True) Then
        cmd.ExecuteNonQuery()
        cmd.Dispose()
    End If

    Me.Visible = False

    Response.Redirect("WebForm3.aspx")
End Sub

the translation of the error is: a semicolon is missing at the end of the instruction