That's right, budgetstoragekin.
One QuickBooks subscription is for one company only. To add another, simply log out of your Intuit account (QuickBooks company) to return to the Sign-in page. Then, click the Sign up hypertext in blue text to select a plan.
After selecting a plan, you'll be asked to create an Intuit account. Since you already have one, just click Sign in on Adding a company to an existing account? Sign in. Then, enter the credentials you use when signing in to your existing QuickBooks company.
You can also check out the detailed steps in this article: Create or add another company.
Please let me know if you have other questions in mind.