Please see How do I transfer prototypes from my personal account to my Enterprise account? for directions on how to transfer prototypes to your Enterprise account. Once the prototype has been transferred, you can select whether the prototype(s) should be viewed by everyone, or specific teams. Simply click the green circle with the people and "+" icons at the top right of the prototype dashboard. Currently, you must do this for each prototype individually, if you are assigning a team or individual access to a group of prototypes.