Step 1: Under System, Click Security Kit settings.
Step 2: Click SSL/TLS to see HSTS settings.
Step 3: Check the box for HTTP Strict Transport Security.
Step 4: Specify the Max-age (in seconds) for how long the header should remain active.
(Optional) Check the box to Include Subdomains for this domain.
(Optional) Check Preload if you plan to submit your domain to the HSTS preload list after saving these changes.
Step 5: At the bottom, click Save configuration.