After disconnecting your Facebook account from the platform, go to your FACEBOOK page settings (https://www.facebook.com/settings?tab=business_tools&ref=settings), remove the app as per the snapshot below:
How to remove app access from Facebook
After disconnecting your Facebook account from the platform, go to your FACEBOOK page settings (https://www.facebook.com/settings?tab=business_tools&ref=settings), remove the app as per the snapshot below: