Not sure if there is support still via the web interface , you can use application CLI to manage the volumes which are part of the application. The cli commands are not available via adanced or admin priviledge , it is available only via diag priviledge , set -privilege diagnostic). Use the below CLI to clean up the volume and it is association with the application,
* application volume show (to get the list of volumes which are part of a given application)
* application -volume remove -volume <volume name> -vserver <vserver name>
* application show-details ( get the objects associated with the application)
* (After removing all the assoicated objects of the application)
* application metadata delete and application hostdata delete can be used to delete the last traces of the application.