you should ask other pros here..
i got it from another reefer here...
it was already feeding when i got it...
alternatively u can take a look at ML...
i got my other mandarin from Henry,
it was trained by Henry to take Henry's food...
i've read of reefers starving their mandarin for a few days in the betta box,
after a few days, they would try squirting some frozen food in..
but thats a risk i wouldnt want to take..
there're many success stories out there,
there are even mandarins who take pellets!!!
maybe other more experienced reefers can chip in?