Hello there, Kerri. If you're using QuickBooks Online Payroll Core, QuickBooks will handle the final submission for you. Just ensure all your employees are paid for the final period, with a process date on or before April 5th. The system will automatically tag and submit the final FPS.
If you're using QuickBooks Online Payroll Advance, when you finalize your last pay run, look for the checkbox labeled This is the final pay run for the tax year. By checking this box, you are officially notifying HMRC that you’re closing the books for the tax year.
Feel free to return to this thread if you have follow-up questions.