You have to feed what they are feeding at first. Then slowly change the diet.
Parakeets are a grass seed eater by nature. I would keep seeds in the diet. But try to have lots of veggies and greens very few fruits. And pellets are good as part of the diet. Others may have different advice. Mine eat seeds, they actually choose on their own to eat some pellets, and they eat veggies of all kinds daily, as well as occasionally scrambled eggs, and acrade treat if while grain bread with seeds in it. Some bird muffins. Mine seem to prefer their leafy greens hung up. They also will eat the yogurt I offer occasionally to my parrots. They even play and chomp on the big bird toys, more so than the parakeets size toys I got for them. And they nibble the mineral blocks more than the other parrots.