@OP
Are you sure you're using openldap old style configuration through slapd.conf?
Chances are that your ldap server uses cn=config, so check under /etc/ldap/slapd.d for a file olcDatabase{X}hdb.ldif and change the olcRootPW value (that's the admin's password), after making a backup first.
Check
this link too, for more details
Regards