Perform the following in the Azure Console:

1. Go to SQL servers
2. For each server instance
3. Click on Auditing
4. Select Storage Details
5. Set Retention (days) setting greater than 90 days
6. Select OK
7. Select Save

Perform the following in Azure PowerShell:

For each Server, set retention policy for more than or equal to 90 days.

set-AzureRmSqlServerAuditing -ResourceGroupName <resource group name> -ServerName <server name> -RetentionInDays <Number of Days to retain the auditlogs, should be 90days minimum>

References:

1. https://docs.microsoft.com/en-us/powershell/module/azurerm.sql/get-azurermsqlserverauditing?view=azurermps-5.2.0
2. https://docs.microsoft.com/en-us/powershell/module/azurerm.sql/set-azurermsqlserverauditingpolicy?view=azurermps-5.2.0
3. https://docs.microsoft.com/en-us/azure/sql-database/sql-database-auditing