From Trash:
• Enter Manage -> Trash page from the left sidebar.
• Select the terms/URLs you want to perform the action on, and at the top, from "Bulk Actions" menu, click Restore URLs/Terms.
From Edit URL:
• From the left sidebar: Manage -> URLs -> click the Edit icon for the URL you wish to restore terms for (or click the edit icon at the top-right of a URL box in URL View).
• Select "Delete/Restore Terms" tab.
• Delete or restore terms by moving it between the Active Terms (left) / Trash (right) boxes and click Save.