How can I add payroll history after the original set up screen is gone?

I'll help you add your payroll history to your QuickBooks Online account, order5.

To do so, let's go to the Overview page. Here's how:

1. Sign in to QuickBooks Online as the primary admin.
2. Go to Payroll and then select Overview.
3. Make sure to add all of your employees paid this year in the Tell us about your team task. Include all employees that no longer work for you. Set up each pay item, deduction, contribution, and tax showing on their pay stubs or reports.
4. select Start next to Add your payroll history, 

For more details, please see this article: Add Pay History to QuickBooks Online Payroll.

Once done, you can now process payroll to QuickBooks Online.

Additionally, I've added an article that'll help you learn more about the steps you should take after moving your QuickBooks Desktop file to QuickBooks Online: What To Do After Migrating the Company File.

Please keep us posted if you need additional help setting up payroll in QuickBooks Online. We're always here to help you out.