Once the cluster is running (what Helm calls a "release"), you can adjust the cluster to stop it, restart it, or resize it, by "upgrading" the release chart, specifying the new value for the number of nodes you want. You upgrade the release using much the same command as you do to start it, except rather than repeating the configuration, you can use the --reuse-values flag. So, for example, to stop the cluster, you simply set the number of replicas to zero, reusing all other parameters:

$ helm upgrade mydb voltdb/voltdb       \
   --reuse-values                       \
   --set cluster.clusterSpec.replicas=0

To restart the cluster after you stop it, you reset the replica count to five, or whatever you set it to when you initially defined and started it:

$ helm upgrade mydb voltdb/voltdb       \
   --reuse-values                       \
   --set cluster.clusterSpec.replicas=5