The work area (user interface) > Workplanes > Workplane sets > Change the owner of a workplane set
  
Change the owner of a workplane set
1. Click Structure and then, in the Workplane group, click More.
2. Click WP Set under Workplane Sets.
3. Click Owner. The Modify Owner dialog box opens.
4. Click New Owner and select an assembly in the Structure Browser.
5. Click OK to complete the operation.