Welcome to Microsoft Q&A forum and thanks for using Azure Services.
As I understand, you want to manage Azure SQL Database long-term backup retention.
With Azure SQL Database, you can set a long-term backup retention policy (LTR) to automatically retain backups in separate Azure Blob storage containers for up to 10 years. You can then recover a database using these backups using the Azure portal, Azure CLI, or PowerShell.
When you enable a long-term backup retention policy, it may take up to 7 days for the first backup to become visible and available to restore. For details of the LTR backup cadence, see long-term backup retention.
Refer: https://www.sqlshack.com/managing-retention-period-of-azure-sql-database-backup/
https://www.sqlshack.com/configure-long-term-backup-retention-for-azure-sql-database/
Let us know if above helps and if you have any queries, thanks.