Accessing a Blackboard organization requires that you self-enroll. This is quite straight-forward.
After logging into Blackboard, select "Community" (to the immediate left of "My Institution").
On the Community page, enter your search term in the field on the left - just one word from the organization's title is enough - and select "Go".
The next page will list all organizations with the search word in its name. Find the organization you want and hover over the organization's ID so that a small round button appears. Click the button, and from the menu that appears, select "Enroll".
On the next page, "Self Enrollment", select "Submit".
Log out and log back into Blackboard. Select the "Community" tab and you will see the organization listed under "My Organizations". You have Participant, rather than Student, status.