PHP set specific line in CSV

I am trying to set a specific line in a CSV file. I tried changing $line, but that (obviously) only changes the variable and not the line. I also tried getting the line number but it´s still a mystery how I can write to this specific line only for me.

My Code:

$file = fopen(WP_CONTENT_DIR."/plugins/coinStats/coin_database.csv","w");

  //Search file; If the number is there, get data. If not, create
  while (($line = fgetcsv($file)) !== FALSE) {
    if (in_array($CoinNumber, $line)) {
      $find = $line;
      $foundResult = true;
      //Change line here?
    }
  }