Do what I do when I have to take a dog or cat to the vet for a checkup or shots. Take a ziploc bag of combined dropping, and ask your vet to run a fecal float. They make money off those, so worth the time. They cannot prescribe meds or wormers for your chicken without seeing it, but they certainly can do a fecal float. If they won’t do a favor for you, you can get a new vet. There are commercial worm testing kits online from Amazon and others for animals and chickens. I do not know how accurate they are, but they are available.