HRM - lI need that a eave request: approved by only a person

hi, in HRM area, Leave request, employees can choose who will validate the leave request, using a dropdown menu.
But I need that users will find in this dropfown menu only 1 employee fo choose from
See picture above: here are listed some employees in the dropdown:

For that user, I have set a supervisor, and same person for “force leave request” but are shown also some other users to approve it when he compile a leave request