Thanks for joining the thread. I'm happy to walk you through connecting a credit card account.
The Add account button was available in the old interfaces, like what Catherine said. For the new one, you'll want to click on Link account beside Update and follow the on-screen instructions to connect a credit card account.
On the other hand, if you'll be connecting multiple credit card accounts in a parent-sub account setup, you'll only need to either connect the parent or the sub-accounts only. Please check this article for more details: About bank or credit card subaccount setup.
Let me know if you have more concerns with connecting your account. Have a good day and take care!