You can manually drag notes up or down to fix "sour" notes or use the "Snap to Scale" feature to automatically lock vocals to a specific key.
While the story is a myth, getting the actual plugin is much simpler. NewTone is a native Image-Line plugin newtone plugin fl studio free download
Below is a breakdown of its existing capabilities and how you can "develop" a custom feature or workflow around it. Core NewTone Capabilities You can manually drag notes up or down