Thanks for getting in touch with us today, @Anonymous,
I can help you add another email for you to access your QuickBooks Online account.
You can create a new login ID by adding a new user for your QBO account. Here's how to do that:
Click the Gear icon from the navigation panel.
Under Your Company, choose Manage Users.
Click Add user.
Select which type of user you'd like them to be and follow the corresponding steps.
Once added, the new user will receive an automated login invitation. If that email has an existing QuickBooks Online user ID and password; the email will prompt you to either use the same ID or set up a new credential. Please be reminded to open the link in the email in a web browser when accepting the invitation.