OSError: [Errno98] Address already in use appears and cannot proceed.

Until Heroku beginners deploy simple applications using Flask!-Qiita

Using the above page as a reference, I am trying to deploy a simple application made with flash on heroku.
However, after $heroku open, an application error occurred and it is stuck.

The following error was observed on the console:

$heroku logs --tail
OSError: [Errno98] Address already in use

Tried
·Restart PC
·Change the port number of app.run(port=5000)
·I didn't understand around the kill command.

We will check and add any necessary information or additional information.
I would like to release this app by March 20th, so please lend me your wisdom.