You can manually write the IBOutlet
property declaration in the @interface
of the custom view subclass, and assuming you've defined the base class of your subview in IB, then you can drag from the outlet circle in the code back to the control in the scene.
It was answered here: Cannot create outlet connections to subviews in Interface Builder (Xcode 5)
or you can try this:
After typing the property outlet declarations manually in the customview.h file I could ctrl-drag-connect them from there to their corresponding UIlabel objects in the interfacebuilder. Works only in this direction!