Use course tools>>Discussion Board>>Use archives
You can change the information about a Discussion Board archive or add threads to it. To do so:
Enter the Discussion Board forum whose archive you want to modify.
Click [Click Here for Archives].
Click the Modify button to the right of the archive you want to edit.
Edit the title or description, text format, or availability, as necessary.
For each thread you want to add to the archive, click the box to the left of it so a checkmark appears.
Click Submit to add the thread(s) to the archive.
Note: Click Cancel to return to the Discussion Board page without saving your changes to the archive.