Should I re-run a payrun if I had forgotten to set up my PAYE ID on QB Advanced Payroll before I submitted it? If so then how do I do that?

Hello Elanorwhitby-me, Welcome to the Community. You can roll back the payroll and then make any changes and then resubmit an FPS with corrections to previous submission being the reason. Information on how to roll back the payroll is available here. Any questions let us know we'd be happy to help further.