The Database Mirroring Monitor is part of the SQL Server Monitor, which is launched from SQL Server Management Studio.
Database Mirroring Monitor is not available in every edition of Microsoft SQL Server. For a list of features that are supported by the editions of SQL Server, see Features Supported by the Editions of SQL Server 2016.
To launch the Database Mirroring Monitor
After connecting to the principal server instance, in Object Explorer, click the server name to expand the server tree.
Expand Databases, and select the database to be monitored.
Right-click the database, select Tasks, and then click Launch Database Mirroring Monitor.
In the Database Mirroring Monitor dialog box, click Register Mirrored Database to register one or more mirrored database.
When you register a database at one partner, the database is automatically registered at the other partner. If the monitor already has connection credentials for the other partner instance, those are used to connect. Otherwise the monitor attempts to connect using Windows Authentication. If you want to change the credentials used to connect to either server instance, click Show the Manage Server Connections dialog box when I click OK.
For more information about Database Mirroring Monitor, see Database Mirroring Monitor Overview.