Note: In Coeus, department are referred to as Units (i.e. "business units"). PEER inherits this terminology, so Department and Unit mean the same thing.
You cannot directly add a new Unit to PEER. New entries must be validated before they are created to ensure information is correct and any additions are not duplicates of existing records.
To request a new Unit be added to PEER, you'll want to submit an Action Request in PEER. Please see the article Submitting an Action Request, and select the Action Request called "Add a Unit to PEER".