@Taen keren, in most scenarios you want your web app to be accessible from everywhere. In this case, it does not make sense to implement IP access restrictions. However, you might want to implement additional security by putting a Web Application Firewall in front of your Web App and restricting access to it only from the WAF IP.
You can/should also protect the Web App's deployment/management endpoint (.scm.azurewebsites.net, a.k.a. Kudu), to make it accessible only from the IP addresses that are trusted sources for deployments.
In any case, if you think you can't/don't want to improve much more your Web App security, then you can always dismiss the Security Center recommendation.