How can I get notified of changes to certain columns in google sheets

Zapier only provides functionality to monitoring rows. How can I monitor changes to only specific columns?

function sendEmailAlert() {  var ss = SpreadsheetApp.getActiveSpreadsheet();  var data = ss.getActiveSheet().getActiveCell().getA1Notation();  var sheetname = ss.getActiveSheet().getName();  var user = Session.getActiveUser().getEmail();  var Toemail = 'my_email@gmail.com';  var subject = 'New Entry -'+ ss.getName();  var body = 'Your file has a new entry in - '+ sheetname +' Updated by - '+ user +' check file now- '+ ss.getUrl();  if(getColumn ==2 || getColumn ==3) {    MailApp.sendEmail(Toemail,subject, body); }};

Following the suggestion here. Just need some tips on what should be inside the if conditions and trigger conditions.