Request User Selecting an Approval

I'm trying to create an off-boarding workflow. HR will be the submitting user, and on creation of the Service Request, they need to be able to select another user in the system. That selected user will be pre-populated in the Manager Task tab where the manager uploads a completed form and marks the tab as complete.

1. How does HR select the manager?
2. How does the manager get notified of a task? (managers are not SysAid Administrators)