see the task answer with step by step below:
Enable Web Application Firewall (WAF) for the application gateway. You can use the Azure portal, Azure PowerShell, or the Azure CLI to do this. You need to select a WAF policy and a WAF mode for the application gateway. You can choose a predefined policy or create a custom policy with your own rules and exclusions.
Configure WAF policy settings. You can use the Azure portal, Azure PowerShell, or the Azure CLI to do this.
You need to select the managed rulesets and rule groups that you want to enable or disable for the WAF policy. You can also configure custom rules to match specific patterns or conditions and take actions such as blocking or logging requests.
Monitor WAF logs. You can use different types of logs in Azure to manage and troubleshoot the application gateway and the WAF policy. You can access some of these logs through the portal, such as metrics and health probes. You can also export the logs to Azure Storage, Event Hubs, or Log Analytics and view them in different tools, such as Azure Monitor, Excel, or Power BI.