Unfortunately there isn't much you can do - the wound is old and would be unlikely to knit back together even if it were fresh. Trees and shrubs don't heal wounds like we do by means of regenerating tissue to seal a cut; instead, they compartmentalize internally, meaning that they build a "wall" of tissue behind the wound designed to block the spread of any infectious diseases, rot, or wood-boring insects from reaching healthy wood beyond. (Incidentally, the only live wood in a tree trunk/branch is closer to the exterior, just under the bark; inner core heartwood is already naturally dead tissue.)

The only intervention an arborist might suggest is to brace the two halves with some sort of stabilizing device so they don't split further in future storms. Since the break only affected a slim section of sapwood on each side, the branches themselves may survive for awhile longer if they don't crack further. You may want to have a certified arborist assess the tree to determine if this is even feasible or worth the cost of materials.

Miri