There is no way to do it on the web app. I sent emails to try have it removed, first one being on the 26th of Feb, all I got was an auto acknowledgement that it was received (Zendesk) and subsequent auto followups telling me the ticket is awaiting my response, even though there is nothing for me to respond to. I sent a follow up mail and still nothing. Has anyone actually managed to get their payment details removed from there?