The SSL renewal process typically involves generating a new certificate signing request, submitting it to the certificate authority, verifying ownership of the website, and then installing the new SSL certificate on the web server.

This article has in detailed guide about SSL Renewal steps - https://sslwiki.org/how-to-renew-ssl-certificate/

SSL renewal is the same as like purchasing new SSL certificate. You can start from the scratch like you can buy new SSL certificate and generate the certificate through a csr and once you validate your domain name, the certificate authority will send you the certificate. You can install it on your website.

Read the detail guide on how to renew comodo SSL certificate, you have:
https://cheapsslweb.com/resources/how-to-renew-comodo-ssl-certificate

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