When you run Prodigy, it starts a regular web server on the given host and port. So you'll need to terminate the web server – otherwise, it keeps running on the port. (This isn't specific to Prodigy btw and you'll be able to stop the Prodigy server just like you'd stop any other server in your notebook).
I think Jupyter Notebooks just let you press the "stop" icon on the cell? Also see this Stack Overflow thread: