im nearly finished the tiens landing part, about to leave on dragonfly. i was wondering after the attack on the school, and leaving tiens landing, can you go back to the spirit cave because i need it for my iron palm scrooll

That's impossible. You can't go back to Two River and spirit cave since there's nothing left in there.
Are you open palm or closed fist? If you open palm, better focus on other powerful style. Or if you really miss the iron palm, I suggest you re-play from beginning.