Using the Full-Face-Fillet command:

The “Full Face Fillet” option is used for rounding or capping ribs and other exterior part features. This option uses three adjacent face sets and allows the creation of fillet geometry which is difficult or impossible to create using traditional edge-based filleting method. The image below shows an example feature using Full Face Fillet.

To generate rounding, you have to select a set of three faces: Left face, Center face and Right face. The Center face will be round face and two adjacent faces (Left and Right) will be tangentially connected with the Center face.

In case you fillet faces with surface sets, you can flip the rounding direction by just clicking the gray arrow in the graphic window.