Writing to a text file at a given line

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C#

Hello,

I know how to write in a text file using the code below. But it adds the given text at the first line. If I want to write at a specific line without affecting its upper lines, what should I do?

Thank you very much

try
           {
               using (StreamWriter sw = new StreamWriter @"E:\Hello.txt"))
               {
                   sw.Write(textBox1.Text);
               }
           }
           catch
           {
               MessageBox.Show("Writing failed");
           }