Blackboard allows you to override a student's enrollment availability in a course so they can continue accessing it until a certain date, even if the course is unavailable.

To allow this access, search for the course and go to Enrollments in the contextual menu. Then locate the student you want to grant access to, and again in their contextual menu, click Edit.

Add the date until which the student will have access in Availability Override Date and save.

This method can be used, for example, to allow a student to finish a course that has officially ended and was closed on the planned dates.