Add the CNAME records automatically if you are using a free subdomain or using infinityfree nameservers (click setup CNAME records automatically). Add the CNAME records to Cloudflare or your DNS provider if you are using external DNS. Then press next
Generate a real SSL through the client area, go to the SSL/TLS section in the control panel and fill the certificate and private key area (delete any contents currently there as that is your self-signed ssl).
FYI: the client area should offer to setup the CNAME record and SSL certificate automatically to your domain. If it doesn’t, that usually means the domain name is not correct.