Are you supposed to let the frozen bloodworms thaw out before you feed them to a betta fish?

i got some bloodworms for blaze ( my red betta fish) today and the "fish expert" at petco told me to cut off a little sliver of the cube and put it in the tank. i got home and tried it and it didnt really turn out like a sliver, more like red/black snow. it sank to the bottom as soon as i droped it in. i just want an answer before the next time i feed him bloodworms