HaruBit, the Korean course app on Google Play, works without an account. If you signed in with Google, you can delete your HaruBit account and all progress stored with it.
This deletes your account and the learning progress and settings synced to it straight away. Progress and settings on your phone stay until you clear the app's storage or uninstall it.
If you can't use the app any more, email support@harubit.app from the Google account you signed in with, and ask for your account to be deleted. We delete the account and everything stored with it within 30 days and reply when it is done.
Nothing is kept after deletion. See the privacy policy for everything HaruBit stores.