To add another replica to the configuration, you simply right-click the Availability Replicas node within the availability group you want to add it to and choose Add Replica. You’ll have to connect to existing replicas first and then identity (connect) to the new replica you want to add.
Then, as you can see in Figure 43.23, you identify how you want this replica to be used in the availability group (read-only Yes for this example). We also want this to be updated asynchronously, so do not check the Automatic Failover or Synchronous Commit boxes. Finish the wizard the same way we did for the first replica (data synchronization, shared network location for backups, and so on).