Hello, you may refer to the below documentation, most user may confuse between Cloudflare Edge SSL and their origin server SSL. If you want to renew your own origin server SSL and having trouble, you need to reach out to the CA provider of your choice, they may guide you the process to renew the SSL certificate.
To bring your own origin server SSL that you purchased from CA into the Cloudflare Edge, you can utilize the custom SSL. Custom certificates are meant for Business and Enterprise customers who want to use their own SSL certificates.