HSTS (HTTP strict transport security) is a very powerful browser. It is a web server directive, which instructs the web browser how to deal with its connection through a response header.  It increases the website security level by ensuring connection over https:// encryption.

To Implement HSTS, follow Some Steps

1)  check the validity of the SSL certificate of your website

2) Redirect all the http:// links to https://

3) Cover all the subdomains with wildcard SSL certificate

4) HSTS header should be served on the base domain for https:// request and set Max-age to at least 18 weeks.

5) Specify preload directives and "include subdomains" directives