how do you get your child back if emergency custody has been placed

There is not enough information to give a coherent answer -- "placed" by whom?  When?  How?  Is there a case pending?  If so, divorce, or abuse and neglect, or some other?  You can look at the resources we have posted on normal custody orders and modifying them: http://willicklawgroup.com/child-custody-and-visitation/ But I think you are going to have to consult with knowledgeable counsel and explain in MUCH greater detail just what the factual background is, what has happened, and how, if you hope to get better answers.