Your customer needs to set up a workflow to direct approval processes to the head...

To direct approval processes to the head of a business unit, you use a Dynamic Role. This approver type allows you to dynamically assign approval tasks based on relationships such as the head of a specific organizational structure.

A Manager approver type refers to direct line managers, which is different from business unit heads.

Dynamic Groups and Roles do not specifically address the dynamic nature of organizational roles like a business unit head.