To Reverse the Direction of Mesh Element Normals

Select the Change Mesh Normal tool.
Select a mode to use.
Select the mesh element.
The mesh highlights, with graphics displaying the current normal of each facet.

These graphical normals are scaled by facet size. If the mesh has attached normals (for example, from the Facet Smoothing tool), these normals are displayed, one at each corner of each mesh facet.