Put your carcasses in the Instant Pot.
Cover with water (make sure to not add too much water). In the video, I say to fill up to capacity but just cover your bones.
Select the Soup function. If your pressure doesn't' have that function, you can manually set the cooking for 30 minutes.
Don't depressurize your Instant Pot, just let it depressurize on its own. You can check after about an hour. When the lid opens easily, the pressure cooker has depressurized. I sometimes leave it to stay warm for many hours.