Note - Create an Approval Workflow before you can attach it to a Department. See: Create an Approval Workflow
1. In [Settings] [Departments] expand the Organisation to see the Departments.
2. Double-click in the space in the [Requisitions Approval Workflow] column in the Department's row and select the appropriate Approval Workflow from the dropdown, then press 'Enter' on your keyboard.
Note - The Organisation should also have an Approval Workflow attached in case users forget to select a Department when creating a Requisition. This Workflow should start with a User that can reassign the Requisition to the appropriate Department.
You have now attached an Approval Workflow to a Department.