Automated backups sql server IaaS
From 


  An Azure storage account to use for storing Automated Backup files in
  blob storage. A container is created at this location to store all
  backup files. The backup file naming convention includes the date,
  time, and database GUID.


https://docs.microsoft.com/en-us/azure/azure-sql/virtual-machines/windows/automated-backup

If you turn that feature off in the portal, you can still use the underlying engine feature SQL Server managed backup to Microsoft Azure, which allows you to specify the container.