Hi Laura104, 

Are you looking to set up a client file under your current QuickBooks Accountant file? If you have a current QuickBooks Company file subscription, you will not be able to add a second company within it , that will be a second subscription to open. 

Let me know,

Thanks

-Steven

@laura104 

One QBO account is for one company file. You may utilize the Class feature to manage divisions or branches. Otherwise, you should open the second QBO account with the same email address.

https://quickbooks.grsm.io/Australia