Hi,

Try this code and it should work. 

var gr = new GlideRecord("incident");
gr.addActiveQuery();
gr.query();
while(gr.next()) {
  var notes = gr.comments.getJournalEntry(-1);
  var na = notes.split("\n\n"); //stores each entry into an array of strings
  gs.print("Entered while loop"+notes);
  for (var i = 0; i < na.length; i++) {
    gs.print(na[i]);
    gr.work_notes=na[i]; 
    gr.update();
  }
  //now delete the additional comments. which we need to do from 3 tables sys_audit, sys_history_line,sys_history_set and sys_journal_field
  var sysaudit_rec = new GlideRecord("sys_audit");
  sysaudit_rec.addQuery("documentkey",gr.sys_id); //incident sys_id
  sysaudit_rec.query();
  while(sysaudit_rec.next()) {
    //now fetch and delete associated history line records
    var history_rec = new GlideRecord('sys_history_line')
    history_rec.addQuery('audit_sysid',sysaudit_rec.sys_id); 
    history_rec.query();
    if(history_rec.next()){
      history_rec.deleteMultiple();
    }
   //fetch and delete entries from sys_history_set.
     var historyset_rec = new GlideRecord('sys_history_set')
    historyset_rec.addQuery('id',gr.sys_id); //incident sys_id
    historyset_rec.query();
    if(historyset_rec.next()){
      historyset_rec.deleteMultiple();
    }
     sysaudit_rec.deleteMultiple();
  }
  var journal_rec = new GlideRecord("sys_journal_field");
  journal_rec.addQuery("element_id",gr.sys_id); //incident sys_id
  journal_rec.addQuery("element","comments");
  journal_rec.query();
  while(journal_rec.next()) {
     journal_rec.deleteMultiple();   
  }
}

Mark the comment as a correct answer and also helpful once worked.