Introduction
Faculty can use these instructions to re-open access to their courses from previous terms. This is frequently used when instructors need to make changes to the People section of their courses and find the "+People" button grayed out.
Steps
Go to the Course Settings.
The Course Details tab displays by default.
Change the Course Participation from Term to Course using the dropdown menu.

Change the Start and End dates by clicking on the calendar icon and selecting a new date.
The Start date is usually completed automatically as the term's first day of classes; select an End date extending into a current or future term.

Scroll down to the bottom of the page and click Update Course Details.

Conclusion
After following these steps, faculty should now be able to fully access a course from a previous term. For further information, please see the Canvas Instructor Guide- How do I change the start and end dates for a course?