The certutil command with the -L (list) an -d (directory) options can be used to list the certificates in your nssdb (Network Security Services Database).

~]# certutil -L -d /etc/pki/nssdb

Certificate Nickname                        Trust Attributes
                                            SSL,S/MIME,JAR/XPI

*.example.com root CA                    CT,,
*.example.com intermediate CA            CT,,
*.example.com                            CT,,

Then the -D (delete) and -n (name) options can be used to delete a certificate.

certutil -d /etc/pki/nssdb -D -n *.example.com