After following this [topic](https://stackoverflow.com/questions/13100139/update-one-column-in-csv-file-c-sharp) I am able to create
the new row but my question is how do 
I save or write the new line to the file?

I tried 'StreamWriter' but it only writes the newly
created line.

Any suggestions please?

Here is my code so far:

```
string path = @"C:/CSV.txt";

string[] lines = File.ReadAllLines(path);

var splitlines = lines.Select(l => l.Split(','));

foreach (var line in splitlines)
{
   if(line[1].Contains("34"))
   {                                        
     line[1] = "100";
     var newline = string.Join(",", line);
     StreamWriter sr = new StreamWriter(path);    
     sr.WriteLine(newline);
     sr.Close();                                      
   }
 }

```