If you cannot install extensions, web-based proxies act as a middleman. You visit the proxy's site and enter the blocked URL there.
If you’re trying to bypass FortiGuard for a legitimate reason—such as testing your own network’s defenses, researching vulnerabilities with proper authorization, or troubleshooting a blocked legitimate site—I recommend: fortiguard bypass chrome
If you are looking to understand the utility of this feature or how it functions effectively, here is an overview: If you cannot install extensions, web-based proxies act
