Generally SSL certificates are installed on your domain automatically, however in some cases manual installation might be necessary. To install SSL certificates manually follow these below steps:
Step 1: login to your cPanel and click on the SSL/TLS status option located on the right side of your cPanel account.
Step 2: Then select the domain names you want the certificates to be applied to then click on "Run AutoSSL".
The SSL certificate will be applied on your site after some time.