Welcome Yak!
The balls you speak of are nutriberries, yes? My little Pascal was really finicky himself with those, I had to crumble them down and offer it to him. Next step was to hold it for him while he is eating it because he is a very young bird and very clumsy, he simply couldn't hold it and eat it. Then I moved up giving a smaller piece that he needs to hold, and later on it became one of his favourite treats, he's a pro now, being a big boy and holding it all by him self and just crunching it down.
Best would be a pelleted diet instead of seeds. My personal suggestions would be either Roudybush or Harrison's, but this also highly depends what is available to you and where are you from.
Harrison's is considered one of the best, fully bio and organic. I like their sizes, they also make super fine pellet which is the size of a millet, which would be a great switch. I switched 3 birds from seeds to pellets, and I realised that size played a huge role. The smaller and more similar in size of the seeds, the better. My only issue with Harrison's is that it is super expencive.
Another one is Roudybush which I mainly use for my budgie and Pascal the little conure, I use their smallest size (nibbles) and they like it. Pascal accepted the pellet within 3 days, I was offering them as if they were treats. It takes a few tries throughout a few days, and so many pretending that you're the one eating it. Once you see that they bird will actualy eat it, try swapping the seeds with the pellets for a few hours per day. Closely watch if the bird eats. Never leave the bird without food (that they will eat) for more than 6 hours!
While Pascal switched very quickly, our foster cockatiel Archie took maybe a month or two, with several tries. I had to pretend with my finger doing the pecking motion in the bowl and he would follow. That's how I managed to switch him. Repeated offering throughout days and months could be the key, one day they just seem interested and start eating. this goes for many other foods, I had to re-introduce veggies for Pascal to eat them.
Usual issue is that the bird doesn't understand that pellet is food, which is why pretending you eat it can be helpful.