Welcome back to QuickBooks Community. I'll share steps to ensure you're able to add several apps in QuickBooks Online.
I suggest going to the Apps menu at the left panel inside QuickBooks Online. From there, you'll have the ability to add different apps. Please know that only Primary Admin and Company Admin users will see the Apps tab within QuickBooks Online.
Click Apps in the left navigation menu.
Click the Browse Category drop-down menu, select Sync Data.
Select the app you want to integrate.
Click Get App Now and complete the following on-screen instructions.