我想覆盖并将新值存储在CSV文件中

Question

我正在根据自己的要求修改CSV文件中的数据，并且能够成功对其进行修改。但是以前的数据不会被删除。我怎样才能做到这一点？

 List csvfiles = new List();
        private void btnimport_Click(object sender, EventArgs e)
        {
            OpenFileDialog openFileDialog = new OpenFileDialog();
            openFileDialog.CheckFileExists = true;
            openFileDialog.AddExtension = true;
            openFileDialog.Multiselect = true;
            openFileDialog.Filter = "CSV files (.csv)|.csv";
            if (openFileDialog.ShowDialog() == System.Windows.Forms.DialogResult.OK)
            {
                foreach (string fileName in openFileDialog.FileNames)
                {
                    csvfiles.Add(fileName);
                }
            }
        }


    public void csvedit()
    {
        string path = @"C:\Users\Sunil\Videos\original\GSK.csv";
        string csvContent = System.IO.File.ReadAllText(path);
        Regex r = new Regex(@"("",""(?=[0-9]{2}\/[0-9]{2}\/[0-9]{4}))");

        var newStr = r.Replace(csvContent, "\n").Trim("\"".ToArray());
        newStr.Trim("\"".ToArray());
        System.IO.File.WriteAllText(path, newStr);
    }

    private void btnexport_Click(object sender, EventArgs e)
    {
        csvedit();
        string installedPath = "C:\\Users\\Sunil\\Videos\\changed";

        //Check whether folder path is exist
        if (!System.IO.Directory.Exists(installedPath))
        {
            // If not create new folder
            System.IO.Directory.CreateDirectory(installedPath);
        }
        //Save pdf files in installedPath ??
        foreach (string sourceFileName in csvfiles)
        {
            string destinationFileName = System.IO.Path.Combine(installedPath, System.IO.Path.GetFileName(sourceFileName));
            System.IO.File.Copy(sourceFileName, destinationFileName);
            MessageBox.Show("File Exported Successfully");
        }
    }