Fulfilling this process is easy: from your Backend, just call Pluggy's Delete Item endpoint (DELETE /items/{itemId}). If successful, a 204 status response will be sent. This confirms that the Item which holds all the references to the user's financial data has been deleted.
Any subsequent call to GET /items/{itemId} endpoint to attempt to retrieve the data of this item, or to any endpoint which would return the Item related financial products, will return a HTTP 404 Not Found response.
Make sure to implement this option in your integration, and have it always available for your users, to be in compliance with Open Banking regulations.