How can I add an FYI notification to the Initiator when the Department Approver approves the invoice

Summary:

Our approval process is two-level, the first level is getting approval from the department approver, and the second level is the central office. How Can I add an FYI box that the initiator will get a notification when the department approver approves the invoice.

Thanks

Content (required):

Below is the step I took:

1. Add a parallel FYI to the second stage FYI
2. In the basic tab: 

Name: FYI

Asignees Based on : Rule-based

Business rule: Create new rule: SecondStage

questions:

1. How can I configure the new rule ?
2. What else do I have to do to make it work ?
3. How do I delete the newly added FYI Participant in stead of ignore it ( I got an error message : can not delete the last remaining participant in a stage )