Firstly you need to let the frozen pieces thaw and to size them just right. Betta have stomachs that are just smaller than the size of their eye so its VERY easy to overfeed them and get them constipated.How can i get my Betta to eat the frozen Brine Shrimp (the ones in cubes). i break some into the water it just floats away.
I've trained my bettas to take food right off my finger. Even when I don't go for the finger method, the females still jump right up if they see my finger above the surface.