best response confirmed by AWSullivan (New Contributor)
Solution

@AWSullivan 

You will need to know the workspace ID. Then use PowerShell. 

Azure AZ module:

https://docs.microsoft.com/en-us/powershell/module/az.operationalinsights/new-azoperationalinsightsa...

 

New-AzOperationalInsightsAzureActivityLogDataSource -ResourceGroupName <LogAnalyticsOMSWorkspaceResourceGroupName> -WorkspaceName <LogAnalyticsOMSWorkspaceName> -Name <NameOfThisOperationalInsightsAzureActivityLogDataSource> -SubscriptionId <Subscription>

 

AzureRM module:

https://docs.microsoft.com/en-us/powershell/module/azurerm.operationalinsights/New-AzureRmOperationa...

 

New-AzureRmOperationalInsightsAzureActivityLogDataSource -ResourceGroupName <LogAnalyticsOMSWorkspaceResourceGroupName> -WorkspaceName <LogAnalyticsOMSWorkspaceName> -Name <NameOfThisOperationalInsightsAzureActivityLogDataSource> -SubscriptionId <Subscription>

 

 

Cheers

 

Craig