If content needs new topic assignments or needs to be moved between topics, you can easily make those changes from the content profile page.
Go to Administration > Learning > Library.
In Library view, ensure your view is still set to Topic.
Find the old topic you wish to move content from.
Click the down arrow on the left side of the topic name to reveal all associated content.
Click on a Content Title to open its specific profile.
On the Details tab, scroll down to the Libraries & Topics section.
Add the New Topic: Type the name of the new topic and select it.
Remove the Old Topic: Click the "X" or delete icon next to the old topic name to remove it from this content piece.
Save your changes.
Repeat these steps for any piece of content you would like to reassign to a new topic.