There is no explicit way to target a single entry. However, you can achieve this in one of two ways:
By creating a bind rule that matches user input in the bind request with an attribute value stored in the targeted entry
By using the targetfilter keyword
With the targetfilter keyword you can specify an attribute value that appears only in the desired entry. For example, during the installation of the directory server, the following ACI is created:
aci: (targetattr="*")(targetfilter=(o=example)) (version 3.0; acl "Default anonymous access"; allow (read, search) userdn="ldap:///anyone";)
This ACI can apply only to the o=example entry, because that is the only entry with an attribute o having the value example.
The risk associated with these methods is that your directory tree can change in the future, and you would have to remember to modify this ACI.