So sorry to hear of your fish dying. The first thing I would do is to make a one third water change from the bottom of the pond to remove excess toxins that have accumulated there. If you have any sludge or other debris at the bottom of your pond, remove it quickly as this could also be a cause to the death of your fish.
Have you had a chance to feed them yet?
If so, what have you been feeding them?

Yours Koily, Lorraine