Const replaceMe As String = "," '
    Const replacement As String = "~"
    Dim line As String = Nothing
    Using r As New StreamReader("a.txt")
        Using w As New StreamWriter("ss.txt")
            line = r.ReadLine()
            While Not line Is Nothing
                w.WriteLine(line.Substring(0, 9) + line.Substring(9).Replace(replaceMe, replacement))
                line = r.ReadLine()
            End While
        End Using
    End Using

aaa,"da,dd",22,22
aaa,"da,dd",22,22
aaa,"da,dd",22,22

How to delete comma from within quotation marks

Save the file again without the comma inside the quotation marks