Go to the landing page for group management
https://max.gov/maxportal/sa/maxhome/groupAdmin/main.action then find the DATA Act Broker Users group corresponding to the agency and role you are interested in. There are three roles: upload, certify, and read-only.
Option 1: To send users an invite link, e-mail them the invite link at bottom (see picture). Once they click the link, you will need to approve them.
Option 2: To add users directly, click "Add Users", then add all prospective users by their e-mail address (multiple users may be added at once).