Hi! This is how I changed the diet of my birds from seeds to Harrison's bird food pellets in only two weeks!
Recipe of the muffins here: (just add the pellets to the mix, and use less flour instead)
https://www.youtube.com/watch?v=2KZj5RZuSBM&t=7s
So far, so good! They have been eating them for 3 months now and they love it! (well, of course they prefer seeds, but I think this is more healthy) :P