There is no button to reboot the appliance (which is rarely needed by the way). In most cases you want to restart vR Ops application or cluster. There is a button for it: login to http://vrops-ip/admin and you will see "System Status" -> "Cluster Status" and a button take the cluster offline or online again. If you want to restart the application on individual node you can click on red/green restart icon in the bottom section.
