Food help

So my babtis alittle over months old. For info he isn't hand raised and was sadly the baby of someone's 3 cockatiels. So I got him from a cage of 7 cockatiels that shouldn't of been in there. Since I've had him he has had major improvements. But one thing I'm having an issue with is food. I got the zupreem naturals and a seed mix' with fresh food and fresh water every day. Problem is he blatantly refuses to eat any pellets and only eats millet (was having it EVERY DAY before me and now once a week treat and for training)

How do yall get your babies to eat pellets.

Another note I am trying the zupreem and then hopefully switching to harrisons brand.