This Exchange Server 2016 article will show you how to add a Database Copy to Exchange 2016 DAG using the new DAG Interface.
Step By Step Guide
As you will see below Microsoft added a new feature to Exchange 2016 which allows you to postpone seeding after you add the copy.
The postpone seeding Is a great feature that allows you to wait with the data seeding in times when the database Is very large or the network Is busy during business hours.
To start the process make sure your DAG Is configured.
Open EMC -> Servers -> Databases -> Select the Database -> … Add database copy
Select the Server and set the Activation preference number.
Note: In the screen below you will see the new feature to postpone seeding, if you tick It the copy will be added but mailbox replication will not start.
Process completed, to check replication and health using the right panel.
Or you can use:
For a complete monitoring guide see the article I published previously.