To create a Diagnostic setting Go to Azure portal > Select App Service > under Monitoring, select Diagnostic settings > Add diagnostic setting> Diagnostic-Settings-Page will open > create the Diagnostic setting by providing a name for the Diagnostic setting> Select your desired destination(s) for the logs> Log Analytics Workspace: Analyze the logs with other monitoring data and leverage Azure Monitor features such as log queries and log alerts> Select the desired log categories to export > Select Save at the top this will trigger App Service to begin sending your logs to the chosen destinations.
There are six log categories in addition to your metrics. The table below lists the log types with its description and availability per OS.
You may use AppServiceHTTPLogs which Access logs from the web server logs.
You may refer to below doc links for more details: