You can use the selection tools to select an interior surface of a model; for example, when you create a surface or when you select a region using the solid offset mesh tool.
To select an interior surface:
In the Selection toolbar, toggle on the Select From Interior Entities tool 
.
Note: The Select From Interior Entities tool is hidden by default. For more information, see “Using toolboxes and toolbars that contain hidden icons,” Section 3.3.2.
Select the interior surface from the viewport.
