Assuming you have the correct "sudo" permissions on plato, execute:

sudo trac-admin /usr/local/share/Trac/projects/ChimeraX session add account-name real-name email

If possible please use the bundle name (lowercase, omit spaces) for the account-name so that it is easy to assign Trac tickets to the appropriate account without the need to look up the account name associated with a bundle.

If the user needs to be able to log in to change tickets, see ​this for adding a corresponding web account, and use the Admin tab (above) to give the user appropriate ticket-editing capabilities.