how to get month old betta fry to eat frozen brine shrimp and fd blood worms?

my fry dont seem to be too interested in these 2 types of food. when they are fed live microworms or vinegar eels they just attack them the same thing when i was feeding live brine shrimp. i dont know maybe they eat it later on when it falls to the bottom but im not sure so i continue to add microworms. i see the fry grab the frozen brine shrimp then spit it out. any suggestions