When I signed up and created an account, I added my first business/main income. How do I add my second and third businesses/incomes?

One QBO/QBSP account is for one business account. You can use an old QB Desktop with a non subscription license to manage multi business accounts.

Adding second and third business accounts or incomes is unavailable in QuickBooks Solopreneur, Dylan. Let me share a workaround you can consider to ensure the effective management of your firms.

QuickBooks Solopreneur is intended for a one-person business, which I agree with Chrea. It provides a more straightforward setup with an enhanced experience for managing transactions, flexibility, and productivity tools. To learn more about the features, refer to this article: Introduction to QuickBooks Solopreneur.

Since your subscription is for a single company file or business, consider purchasing a new QuickBooks Solopreneur or subscribing to QuickBooks Online. Please check this page for the plans and pricing: Plans for every kind of business.

Moreover, QuickBooks Solopreneur automatically classifies your incoming bank transactions. However, you can change the category as required.

Furthermore, you can use this tax form to report income, deductions, profits, and losses for your business activities: Schedule C and expense categories in QuickBooks Solopreneur and QuickBooks Self-Employed.

Let me know whenever you need extra help managing your business growth and income entries. I'll be here to assist you. Have a great day!