In QuickBooks Online (QBO), you can add an owner depending on how they contribute to your business. In most cases, the system usually uses suppliers as a way to track owners. Here's how:
Sign in to QuickBooks.
Go to Suppliers.
Select New supplier.
Complete the fields in the Supplier Information window.
Hit Save.
For more tips about the process, you can open this article: Add an owner or partner to your books. The same resource gives you details on how to add an account to track an owner's investment.