Change automated backup settings for Azure SQL Database
Change short-term retention policy
You can change the default point-in-time recovery (PITR) backup retention period and the differential backup frequency by using the Azure portal, the Azure CLI, PowerShell, or the REST API.
To change the PITR backup retention period or the differential backup frequency for active databases by using the Azure portal:
Step 1: Go to the logical server in Azure with the databases whose retention period you want to change.
Step 2: Select Backups on the left pane, and then select the Retention policies tab.
Step 3: Select the databases for which you want to change the PITR backup retention. [Select db1] Step 4: Select Configure policies from the action bar.
Step 5: To change the retention period for point-in-time restore backups, use the slider under Point-in-time restore.
Step 6: To change differential backup frequency, select 12 Hours or 24 hours from the drop- down menu under Differential backup frequency . [Select 12 hours]

Reference:
https://learn.microsoft.com/en-us/azure/azure-sql/database/automated-backups-change-settings