Hello,
maybe its just some wording but with Promotion Management you dont "migrate" reports, you transport them. A migration (f.e. from BOE XI 3.1 to SAP BI 4.2) takes place with the Upgrade Management Tool (UMT).
So if you want to transport them you should check the SAP BI Administrators Guide. In there Promotion Management is pretty well explained.
Regards
-Seb.