Sadly, our dynamic worker image ships, by default, with Helm 2.9.1. It is possible to update this on your worker as part of the deployment process, by running a script step to
choco upgrade kubernetes-helm
which will upgrade it for the life of the worker lease. Naturally, it will not persist between leases, so you would need to keep it there for the time being.
Saying all this, we do have a new feature coming out in the near future, called tooling containers, that will allow you to specify the tools that the deployment will use. You can find more details of this on our roadmap here: https://octopus.com/company/roadmap