istio.io/content/en/boilerplates/helm-backup.md

Before upgrading Istio in your cluster, we recommend creating a backup of your custom configurations, and restoring it from backup if necessary:

{{< text bash >}} $ kubectl get istio-io --all-namespaces -oyaml > "$HOME"/istio_resource_backup.yaml {{< /text >}}

You can restore your custom configuration like this:

{{< text bash >}} $ kubectl apply -f "$HOME"/istio_resource_backup.yaml {{< /text >}}