It's good to see you here in the Intuit Community, GMP1,

Let me get the help you need to ensure you'd able to access your QuickBooks Online (QBO) and QuickBooks Self-Employed (QBSE) account.

Having the same login credentials is not a problem.

To access your QBO account via web browser, use this link: https://qbo.intuit.com.

To access your QBSE account via web browser, use this link: https://uk.selfemployed.intuit.com/login.

Upon logging in to your account, make sure to log in using your login credentials when you sign up for the service.

That's it! Please let me know how it goes, I'm always here to help. Have a great day!