This is very easy as there is an SSL section in the cPanel which allows the creation or upload of the certificate and private key. It’s also where we will be installing the certificate.
In the cPanel, click on SSL/TLS
Go to the “Private Key (KEY)” page and UPLOAD the key you generated earlier
Make sure that your website works by loading it using https.
Edit:As mentioned in the comment section, you should make sure that your website uses ‘https://’ URLs so you may want to add redirects rules and check that all content is loaded from secure URLs.