Transaction approval how to delegate at a user level another employee?

Summary

Transaction approval how to delegate at a user level another employee?

Content

Hello,

One of the approvers in the approvals flow, an employee is leaving .
We will update the approvals flow accordingly , with another employee who replaces him.
In the meantime - How can we delegate to have instead of a user ANOTHER user to approve all his transactions? (the employee's who is leaving transactions ), at the user level?
(without entering each approval flow and click on delegate).
** using the old ui
​Thanks 
Revital.