When you add a new employee to your TalentHR domain, you will need to define that employee’s Manager.
The only exception is in case you've selected "This person is the head of the org." under the Manager field when adding an employee to the system. This will make the new employee the "root" of your organizational chart. The head of the organization does not have a Manager.
If you'd like to give the employee administrative access to all functions of the domain except subscription once you've added them to your domain, you can make them an HR Manager by following the steps here.