Pumpkin or the seeds does not work as a dewormer. It would be great it is did, but it doesn’t. Having wry neck, I would also add human vitamin E 400 IU daily into his beak. Wry neck is another possible symptom of Mareks. Casportpony has a good thread about feeding tubes and sizes. They are available online, and your vet might sell you the tubes and syringes. Walmart and other pharmacies will sometimes give away needle-less syringes free for giving low dose medicines and water to animals and babies. You can give 1 ml safely with one of those down the right side of the chicken’s throat.