Thanks for visiting the Community, @fran15. I can point you in the right direction in setting up your start date for a workplace pension.
You can visit the Pensions Regulator website for more information or you can also use their online tool to guide you on how to enter the start date.
For your reference, read through this help article: Workplace pensions in QuickBooks Online Standard Payroll. It gives you all the information you'll need to know about Workplace pensions.
Let me know if you have other concerns. We're always delighted to assist you some more.
