You can use Apple Business Chat to contact support for your Apple Card. Apple Business Chat is a service offered through iOS which allows iPhone and iPad users to easily contact companies through the Messages app.
All Apple Card transactions and support are handled through the Wallet app. To contact Apple support for any questions or issues involving your Apple Card, open the Wallet app on your device, then tap the three dots in the upper-right corner. From here you can contact Apple support through Apple Business Chat, on the web, or via phone.