You can enroll a user into your archived course two different ways.
From within a Course
From the User's Account Information page
Enrolling within a Course
Navigate to the course you need to enroll a user in.
Once in the course, select Settings from the Course Navigation menu.
Under the Users section, select the +Add Users to Course link.
Select the user to add to the course.
Click the Use Selected button
The user will appear listed under the Users section.
Enrolling within User Account Information page
Select Users & Roles within the Navigation menu.
On the User's tab, select the User's Account, that you would like to enroll in a course
Select the Enroll in Course link
Select the course(s) you wish to enroll the user in
Click Use Selected
The list of courses the user is enrolled in will appear in their Account Information page.
Note:
To unenroll a user from a course, follow the same process but unselect the user from the list.