To add an availability replica to this availability group, you will need to: Connect to all the existing secondary replica ...

To add an availability replica to this availability group, you will need to:
•   Connect to all the existing secondary replica in the availability group.
•   Specify the instance of SQL Server that will host the new replica.
•   Select your initial data synchronization preference.
•   Check the validation results of adding the new replica to the availability group.
•   Review your selections.