Thanks for the clarification, Rjwbailey. I'd like to help you from here.
The unlock process is unavailable in the Standard payroll subscription. You'll have to delete and re-run the payroll. This process will not create a duplicate FPS. Once you delete the paychecks, the FPS will be deleted in QuickBooks, whether it is or not submitted to HMRC.
Here's how to delete a pay run:
Let me share the article about deleting a pay run in QuickBooks Online Standard Payroll to help you learn what happens when you delete paychecks.
Regarding the unscheduled payroll, I know this will be a convenient option in QuickBooks Online. I'll help you by sharing it with our management team. This will be submitted to our management team for review.
If you need something else, please don't hesitate to drop a comment below.