If you make use of our sub-workspace feature, you can move content from the knowledge library from one sub-workspace to another.
On the knowledge library (listing) page, as you view your content, you can see the main/parent workspace (or sub-workspace) to which records belong. Select the checkbox next to a record (or multiple records) to move the selected content to a specific sub-workspace.
Once you have selected knowledge records, select the main workspace or sub-workspace that you wish to move the knowledge to and click "Move these Knowledge items".
Keep in mind that if you move content, you may impact the visibility others have to that content.