@Mentee ,
The feature you are looking for is called horizontal scaling which basically creates 3 separate DDBs Files, VMs and Databases under 1 global DDB. As far as the procedure is concerned, all you need to do is ensure that the option “Enable Horizontal Scaling of DDBs” is enabled. As long as this option is enabled and you have all 3 types of backups associated with the storage pool/policy, this should automatically happen.
https://documentation.commvault.com/11.26/expert/11020_media_management_configuration_deduplication.html
Please note that this option is global so it will happen across the board for all your DDBs. So once a particular threshold is met, you will start seeing multiple DDBs even across the existing DDBs.
Hope this helps!