In your workplace or user settings (editable from Preferences -> Open Settings (UI) from the command palette, or Preferences -> Settings from the application bar), add the following fields:
linkerd-path: Path to the linkerd binary on your system. Required!
linkerd-namespace: Namespace where linkerd may be found in your Kubernetes cluster. Default: linkerd
Note: If linkerd is not found in this namespace, the extension will default to installing in this namespace.