A backup file of a cluster node should only be used in the highest emergency of a full-out scenario. If at least one node remains operational, the cluster should always be reestablished from the last good node.
To recover as much of your data as possible, start by identifying the last good backup you have available from an Active node by analyzing the outage. For example, if the connection to a disaster recovery site went down long before a backup was made there, you might be better off with an older backup from the primary site after such outage.
Once you have identified the best possible backup from a previously Active node N, restore the backup to the Hardware Appliance designated to be node N and then reconnect the other nodes to this node.
For information on how to restore a backup to a Hardware Appliance, see Restore System from Backup.
After reboot, the WebConf will be reachable and operational, but the database will refuse to start up in this situation, hence the applications will not yet be operational. Use the WebConf button Force into Active to force the cluster to continue operations from the restored data set.