As part of creating an Event Hub/IoT Hub/Event Grid data connection to Azure Data Explorer cluster, you specify the default table to which the ingested data goes. So far, the target database was always the database associated with the data connection.
Now, you can dynamically route the data to an alternate database, by setting the Database ingestion property. For security resons, this option is disabled by default. To send the data to a different database, you must first set the connection as a multi-database data connection.
Read more about routing event data to an alternate database: