It is an open navel, with yolk extruding. At this point the choices are cull or try to keep it from protruding more, as eventually it will push intestine out as well.
Have a surgical butterfly bandage and a tube of bacitracin or neosporin at hand. A helper will also be very handy if you can get one.
Wash your hands very well, and hold the chick comfortably and securely, Place a drop of neosporin on your index finger tip, and gently press the yolk back into the navel. Once in, gently pinch the skin surrounding the navel, and while pinching, pluck or trim a little down on both sides to clear a place for the bandage to stick. Place the butterfly bandage across the navel, securing it to the abdominal skin on both sides.
When released, the abdominal skin will hold the tension of the butterfly bandage, and will help to keep the yolk inside until it is absorbed. The navel should close once the yolk absorbs. Leave the bandage in place until it falls off.