If your new Blackboard course site was copied from another course that used Lockdown Browser, you will need to open the Respondus Dashboard at least one time in the new course. A message will appear to let you know that Lockdown Browser can now be used with the deployed exams that were copied with the course.
The Respondus Dashboard can be accessed from the course menu by navigating to Course Management > Course Tools > Respondus Lockdown Browser.