Log on to Blackboard and enter your course. Once you are in your course click Users and Groups and select Users.
On the Users page, select Not blank option from the drop down list then hit Go button.
Now, you can see all the enrolled users listed below.
Find the user that you want to change role, click on the down arrow button next to the username and select Change User's Role in Course option.
Select a role for this user. Make sure the Availability is Yes
Click on the Submit button.
You will see a massage: Success: Role edited.