Fortigate vulnerability

I run pci dss security scan, and my fortigate 600c, with 5.2.11 fimware, and found vulnerability:

HTTP Security Header Not Detected HTTP Security Header Not Detected

RESULT: X-XSS-Protection HTTP Header missing on port 443. GET / HTTP/1.0

THREAT: This QID reports the absence of the following HTTP headers according to CWE-693: Protection Mechanism Failure: X-Frame-Options: This HTTP response header improves the protection of web applications against clickjacking attacks. Clickjacking, also known as a "UI redress attack", allows an attacker to use multiple transparent or opaque layers to trick a targeted user into clicking on a button or link on another page when they were intending to click on the the top level page. X-XSS-Protection: This HTTP header enables the browser built-in Cross-Site Scripting (XSS) filter to prevent cross-site scripting attacks. X-XSSProtection: 0; disables this functionality. X-Content-Type-Options: This HTTP header prevents attacks based on MIME-type mismatch. The only possible value is nosniff. If your server returns X-Content-Type-Options: nosniff in the response, the browser will refuse to load the styles and scripts in case they have an incorrect MIMEtype. Content-Security-Policy: This HTTP header helps to detect and mitigate certain types of attacks, including Cross Site Scripting (XSS), packet sniffing attacks and data injection attacks. Public-Key-Pins: The Public Key Pinning Extension for HTTP (HPKP) is a security feature that tells a web client to associate a specific cryptographic public key with a certain web server to decrease the risk of MITM attacks with forged certificates. Strict-Transport-Security: The HTTP Strict-Transport-Security response header (HSTS) is a security feature that lets a web site tell browsers that it should only be communicated with using HTTPS, instead of using HTTP.

How to fix it ?