If possible, take a sampling of fresh droppings to your vet for a fecal float, this test will tell you if they need deworming.
Basic look over is to check for lice/mites, see that crops are emptying overnight, that they have adequate room in their housing and are eating a nutritionally balanced poultry feed for the majority of their diet.
If you lose another bird in a short period of time and want to find out more about the cause, refrigerate the body and take or send it to your state lab. They will give you are report on their findings.
https://www.metzerfarms.com/poultry-labs.html