GoDaddy SSL certificate on subdomain managed by CloudFlare

Hi,
I have a certificate issued by GoDaddy which covers domain begin managed by CloudFlare. I would like to add another certificate to subdomain pointing to Nexcess server. I would really appreciate for steps to setup this.
Thanks in advance,

The Nexcess server will need its own cert as well. If you can’t get one from Nexcess, you can use a Cloudflare origin cert.