Why switch to pellets
An all-seed diet is high in fat and low in many vitamins, which over time leads to health problems. Formulated pellets give more balanced nutrition, which is why most avian vets recommend a pellet base plus fresh vegetables.
Make pellets appealing
Try mixing pellets into the seed, offering them warm or with a little fresh food, pretending to eat them yourself (birds are curious), and offering pellets at your bird's hungriest time of day. Patience wins — forcing the change is dangerous.