I have access to a k8s cluster with tiller and a Helm chart. I can get all the Helm values. I need to update one of those. I know how to do that normally, i.e. when I have the chart (Chart.yaml, templates/blah.yaml etc. etc.). I don't have those things, but I imagine Tiller does, correct?

How do I update the value when I don't have the chart, or how do I download the chart from tiller so I may update the value with helm upgrade --reuse-values --set key=val <release> <path/to/chart>?

helm get does not appear to get the chart in a usable format.