The best person to contact is Sonja Haerkoenen, but the generic email openaccess@cardiff.ac.uk will work just as well. There is a useful chart to help guide you at:  https://ilrb.cf.ac.uk/openaccesschart/ – it also has a link to the application form.  There’s a lot more information on the open access webpage here as well:  https://intranet.cardiff.ac.uk/staff/research-support/open-access/open-access-publishing