Welcome back to the QuickBooks Community, colintourick. Let me help you achieve your goal of adding a company file in QuickBooks Online.
You can have several companies using the same QuickBooks Online login credentials. However, adding a third company requires you to get a new subscription in order to create one. A single company file is equivalent to one subscription, especially if each business has separate tax reporting.
Then, visit the QuickBooks pricing page and choose the subscription option you want. When you are on the login page, select the Sign in link next to Already have an Intuit account? With the same credentials you have for your current company. If you want to have two separate sets of credentials, enter a new user ID.
Once done, you can go ahead and click the Gear icon at the top and you'll have the option to click the Switch Company from there. For further details, you can click on this article: Create or add another company file to QuickBooks Online.
Lastly, I'm also adding this article to further guide you in effectively managing your business using QBO: Help guide for QuickBooks Online. It contains topics about advanced accounting, banking, and payments to name a few.
Let me know if there's anything else you need help with managing your subscription or account. Know that I'm always here to help you anytime. Take care and keep safe!
