To do this, follow the steps below:
Log into your cPanel
Navigate to the Security section
Click on Let's Encrypt SSL
Next, where your domain is, click on Issue (under action)
Uncheck the subdomains that are not pointing to your server
Scroll down and click on Issue (blue bottom)
This will issue your SSL certificate to the site
The next step is to redirect your HTTP to https, you can do this from your domain section using this link or file manager using this link in your cPanel, after using either of these steps, refresh your site.