if you upload your capx will be easier to help you ^^
if you want to fly put 8 direction behavior on your player and do events like this:
system :on start of layout --> player : 8direction disable,Platform enable
keyboard: press (anything) --> player :8direction enable,platform disable
so now if you press the key you choose you will fly ^^ even you can change that key as if player collision with something or whatever you want