Extending a course is an instructor level permission. You will be creating a new section of the course name INC or incomplete. If you just modify the end date for the course, all students will see the course on their dashboard! Below is a video describing the process.
After watching the video and creating your new section, your students may have problems submitting assignments. This is due to the Available from and Until dates [BLUE] being set for the assignments. Follow the setups below to add the new section to the assignments.