Thank you for visiting the QuickBooks Community again, thomas3762. I can see how important to add the class to the existing check or payroll expense. I'll ensure you can send feedback so our product developers can consider adding the feature you need in the next updates.

Assigning classes to previously submitted checks or payroll entries is currently unavailable, due to the inability to make changes to payroll transactions already processed with Intuit.

For now, I suggest going to the Gear icon in QBO and choose Feedback from there. Then, submit a request about having the option to allocate a class to the created checks in QuickBooks. Any recommendations are sent to our engineers for consideration in future updates.

Lastly, you may refer to this article to see steps on how you can run different payroll reports that you can use to view useful information about your business and employees: Run payroll reports in QuickBooks Online Payroll.

Keep me posted if you need further assistance managing a class in QBO. I'm always around to help, thomas3762. Have a great day!