How to save Note item modification

I am creating my Notes app using Core Data.

I am successfully creating New Notes using the following code:

let note = CoreDataHelper.newNote()
        note.noteTitle = noteTitleTextField.text ?? ""
        note.noteContent = noteContentTextView.text ?? ""
        note.noteDate = Date() as NSDate
        CoreDataHelper.saveNote()

However, how do I let the user save modifications on an existing note (vs. creating another new note)?

Hope someone can help. Thanks!