My reference is the SAP B1 Mobile App for IOS document from SAP website.
"To hide the alerts you have viewed, shake your device. To unhide the viewed alerts, tap "refresh" button" (http://help.sap.com/download/businessone/mobileapp/B1_MobileApp_Guide.pdf)
The Approver only wants to see those documents which are still pending for approval. My client requires that documents that were already approved by the assigned Approver should be deleted from the list.