Best practice on ending PSU and Payroll Relationship

Summary:

We moved one of our Payrolls to 3rd party and it's managed outside of the system.

We want to make sure that the old Payroll details won't be available to see for Payroll users hence looking for guidance on best practice.

My understanding is that we need to end date Payroll definition and PSU for that payroll.

Does anyone know where I can find step by step guidance on this?

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