Set trigger in script in Google Sheets programmatically

Question

I am trying to get a Google Apps Script to trigger on edit of a particular cell. Right now I have achieved this using a run-time trigger option built in Google Sheets. However, I lose the run-time trigger when I make a copy. Hence, I have managed to find a programmable trigger from various sources and patched something together, but it is not working. I have no programming knowledge, so I am unable to understand where I am going wrong.

My objective is to run the script when user edits the Named Range "monthfilter".

With script trigger creation

function HideColumns() {
  //open the current spreadsheet and get the value of the named range and trigger project
   var ss = SpreadsheetApp.getActive();
   ScriptApp.newTrigger("monthfilter").forSpreadsheet(ss).onedit() 
   var name = ss.getRangeByName("monthfilter");
   var namevalue = name.getValue();

My previous function:

function HideColumns() {
  //open the current spreadsheet and get the value of the named range
  var ss = SpreadsheetApp.getActive();
  var name = ss.getRangeByName("monthfilter");
  var namevalue = name.getValue();

  //show or hide February
  if (namevalue == "February") {
    var sheet = ss.getSheetByName("MIS");
    sheet.hideColumns(30);
    /** other stuff */