Employee Records -> View Team and click on employee name to access profile.
Navigate to Work tab.
Select the Reports To field and search for the name of the manager in question.
Navigate to the aforementioned manager's profile and under the Reports To field, select the option: Manages Time-Off if this employee is a manager and has a team to approve/reject time off requests for. '
If they are not the final decision maker for their team requests, then select the next check box. If they are the final decision maker, you only select the first one.
You have to the potential to assign multiple layers to the hierarchy - all that's required is to assign the chain of command on each employee's Work profile.