function onEdit(event)
{
  var timezone = "GMT+1:00";
  var timestamp_format = "HH:mm dd/MM/yyyy"; // Timestamp Format.
  var updateColName = "Part No.";
  var timeStampColName = "Raised";
  var sheet = event.source.getSheetByName('Fill in List'); //Name of the
sheet where you want to run this script.


  var actRng = event.source.getActiveRange();
  var editColumn = actRng.getColumn();
  var index = actRng.getRowIndex();
  var headers = sheet.getRange(1, 1, 1,
sheet.getLastColumn()).getValues();
  var dateCol = headers[0].indexOf(timeStampColName);
  var updateCol = headers[0].indexOf(updateColName); updateCol =
updateCol+1;
  if (dateCol > -1 && index > 1 && editColumn == updateCol) { // only
         timestamp if 'Last Updated' header exists, but not in the header row
         itself!
    var cell = sheet.getRange(index, dateCol + 1);
    var date = Utilities.formatDate(new Date(), timezone, timestamp_format);
cell.setValue(date);
 }
}