If you have an overlap that has split you could try a good contact adhesive like Evostik.
If it is straight break in the material, try a waterproof patch - much the same way as one would repair a bicycle inner tube.
Or buy a new pair.
If they are rubber then as suggested a puncture repair patch.If they are PVC nothing much will stay bonded due to the plasticiser in the material softening any glue you use.