Help! unable to trigger the instances form array

i got one problem here…
i got a array which stores some elements, in string form, and these elements actually represent the name of the instances on the stage. now i want to trigger the instance to reset it’s alpha value…
how i dont know how it works.

i got an array[“A”.“B”.“C”];
Instances name available: A,B,C,D…Z
now how i should do to make the instance A to got triggered?? i call them by using on button.

i try some like[0]=_alpha=0;
but not success.