Hi Mark,
You are right. I figure it out the ACI to add is:
(targetattr="userPassword") (version 3.0; acl "Allow proxyagent updating their password"; allow (write) userdn="ldap:///cn=proxyagent,ou=profile,dc=mycompany,dc=com";)
I used LDIF file to add above to the ACI attribute for 'ou=People,dc=mycompany,dc=com'
Thank you,
- Xinhuan