Click Viewpoint tab > Sectioning panel > Enable Sectioning .
Navisworks opens the Sectioning Tools tab on the ribbon, and draws a section plane through the model in the Scene View. Default alignment for Plane 1 is Top. Default position is through the center of the visible area of the model. Move is the default gizmo.
Drag the gizmo to position the current plane as needed.
To save the current sectioned viewpoint, click Sectioning Tools tab > Save panel > Save Viewpoint .