Press the blue "see inside" button and then the sounds tab, then the microphone and then the circle to record a new sound. Press the orange "Remix" button to remix. You need to record the practise lines for the character you want. Sorry, but I will be doing Starkit. You can find the (draft) animation here: https://scratch.mit.edu/projects/109649878/ Press space to see all the screens. If you want to audition for a part of the opposite gender, go ahead! It could still be used in the animation!
I do not own Starkit's prophecy, I am just animating it.