Ah, sorry I overlooked you were asking about Grafana.
Two options:
1. Use the CLI as the article says (http://docs.grafana.org/administration/cli/)
The CLI binary is available inside of the plugin bundle. So it would be somewhere like this location:
/Library/Application Support/Perceptive Automation/Indigo 7/Plugins/Grafana Home Dashboard.indigoPlugin/Contents/Server Plugin/servers/grafana/grafana-cli
I've never done this myself, let me know how it goes.
2. You can simply delete your Grafana database (it's located in the data directory you configured for the plugin), and restart the plugin. The password will be the default password again, but your data sources and dashboards will be erased. Before you do that, if you have a dashboard you want to keep, you can enable anonymous access via the plugin config, view your dashboard, and export it to JSON.