These users are created only to access your website program. For example, you would create users to log into your WordPress, Joomla or MediaWiki site.
Resetting these user passwords are done through the specific program you're using to run the website.
Below are some links to external sites for the respective application you may be running:
DreamHost has no control over the application user passwords. Because of this, support is not able to provide details with the password or reset it for you.