Click on the magnifying glass on the right side of the hosting package containing the domain name you would like to update.
Near the bottom of the Manage Product page, you will see a button Login to Plesk Control Panel. Click this button.
This should automatically login to your Plesk Control Panel. If not, login with the supplied username and created password.
On the Websites & Domains tab of Plesk, expand the domain details by clicking on it.
Under Security, you will see a link for "SSL/TLS Certificates". If this says Domain not secure, you have not yet installed an SSL certificate for the domain. Click on it.
You will see a blue button "Get it free" under Entry-level protection. This is a Let's Encrypt DV Wildcard SSL Certificate included with your hosting package. It covers your domain name and all subdomains. Click on the blue button.
Confirm your valid email address, and check which subdomains you want secured as well. Click on "Get if free".
It may take a moment to install & configure the SSL certificate. Please don't refresh or hit back on your web browser.
Once secured, you will be brought to the SSL/TLS Certificate settings for the domain.
1 - Automatically redirect all visitors from http:// to https:// (suggested).
2 - HSTS (HTTP Strict Transport Security) is a policy mechanism that helps to protect websites against man-in-the-middle attacks such as protocol downgrade attacks and cookie hijacking. This is recommended to be on, only after it's confirmed that the secure version of the website is working properly.
3 - Keep websites secure automatically keeps the domain and all subdomains secured with an SSL certificate. This is recommended to be on. All subdomains must be secured in order to enable this.
4 - OCSP (Online Certificate Status Protocol) Stapling is a standard for checking the revocation status of X.509 digital certificates. This will allow your website to load faster and aims at improving security and performance (suggested).
5 - The SSL status of each subdomain.
6 - This will reissue the SSL certificate. If you are having an SSL error on your website, and it is already secured, this is a good first method for resolving the issue.
7 - Unassigning the certificate will remove encryption for the website.
8 - Advanced settings.
9 - How long the certificate will remain valid until, and if it will automatically renew.