In the MacOSXx86 version, (I am not sure about any other since I only use this one), the line to edit it.
Code:
sudo /opt/zimbra/openldap-2.3.21/libexec/slapd -l LOCAL0 -4 -u zimbra -h "$my_url" \
-f /opt/zimbra/conf/slapd.conf
and replacing the $my_url with ldap://:389
TTFN