How to install BEL linkerd viz with Helm?

How do I install BEL linkerd viz with Helm? The installation docs don’t say anything about extensions.

The upgrade docs just say:

If using Helm, the procedure is similar to the control plane upgrade, using the respective charts

but it’s not clear what that means. Upgrading the control plane requires using a new helm repo: helm repo add linkerd-buoyant https://helm.buoyant.cloud. Is there a different repo required for BEL extensions?