The admin user has created an second user info for me. However, there is no plus button to input the new user name when open the file.

Let me help you add a new user to your QuickBooks Online account, holly.tang.

The admin user of the account can invite or add you as a new user by going to Gear icon (⚙). Let me show you how: 

1. Click on the Gear icon between the magnifying glass icon and the help icon. 
2. Tap on Manage users and select Add User to start adding a new user to the account. 
3. On the window that appears, set the user type and then click on Next.
4. Then, the user's access rights, tap on Next to set the user settings. 
5. Once done, set the first name, last name, and email.

Then, the new user will now get an email from quickbooks-email@intuit.com on how to create the account. 

Here's more information on this article: Add, delete, or change user access. 

Feel free to let me know if you have additional questions. I'm always here to answer them and help you out with other concerns. Take care and have a wonderful day.