You will receive a notification when there is a new dispute case that needs addressing. The documentation you receive will have information about the dispute as well a unique barcode identifier that will help identify your case when you submit it for processing. For more information, see Why does my notification letter have a barcode?
There are also a few ways to check for new cases using the Merchant Portal.
Within the Disputes Application, all new cases will automatically appear at the top of My Work Queue.
Within the Reporting Application, you can run a Chargeback or Retrievals Received Report.