Good thing to do is this case is do a good size water change, as large as you can, and run some carbon. Also add some Seachem Prime to neutralize the ammonia which may be present from the dead puffer. Keep an eye on the Anemone. Can be very toxic to have it die in the tank. If you see it start to disintegrate, then sick it out and all the gunk around it with a good straight into a bucket. Don't try to get it out it will make a mess.
Sent from my SM-J700P using Tapatalk