Facet Modeling > Facet Handling > Flip Edge > To Reverse the Orientation of Two Facets
  
To Reverse the Orientation of Two Facets
1. Click Facet > Edit Facet > Flip Edge.
2. Select an edge shared by two facets.
The two facets form a quadrangular area. This command replaces one diagonal of this area with the other, changing the orientation of the two facets.