What's the correct way to add custom values to a Helm chart?

Okay one more question as I think it’s best not to assume that I’m doing anything correctly!

The Helm chart that I’m looking to deploy (Apache Superset) requires (at a minimum) that users pass one custom variable during installation (SECRET_KEY).

The documentation says that the variable can be added directly to the Helm being installed.

Is that an acceptable method of doing this in Rancher or is there some other methodology envisioned?