There is, intentionally, no way to iterate over all stored objects or query them in any way in Swarm itself without administrative credentials. No one can access your data unless he has its UUID or name (in case of named streams).
You can use the optional Swarm Search functionality to enumerate the cluster. This uses an external search engine to store information about your objects (and their custom metadata) which can then be queried. See the Swarm Guide for details.
There is a way to iterate volumes one at a time using admin credentials, but this doesn't scale for volumes with lots of streams and can take a very long time. Please contact Tech Support if you need more information about this, but typically Tech Support will suggest setting up a Swarm Search cluster instead.