There are two solutions to this issue:
1) You can regenerate the default self-signed certificate using OpenSSL:
openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout /etc/pki/tls/private/localhost.key -out /etc/ssl/certs/localhost.crt
2) You can search the Apache config files and replace the self-signed cert with the new certificate.
This command will tell you which Apache config files reference the localhost.crt file:
grep -i -r localhost.crt /etc/httpd/
An example output of the above command might be this:
That tells us to look in /etc/httpd/conf.d/ssl.conf and update the SSLCertificateFile, SSLCertificateKeyFile, and SSLCertificateChainFile to their new DigiCert certificate files.
Please feel free to call DigiCert support at 1-801-701-9600 if you have any problems or questions.