Here are some examples of how to use "erstwhile":
* "The erstwhile champion has now retired from competition." (The champion was once a champion, but now is not.)
* "The erstwhile bustling market is now a quiet, forgotten place." (The market was once busy, but now is not.)
* "She was an erstwhile student at the university, but now she works there as a professor." (She was once a student, but now is a professor.)
The word "erstwhile" is often used to emphasize a change in status or situation. It can also add a sense of nostalgia or regret for what was once.