This feature is available in Enterprise and Ultimate editions.
You can move (or reassign) workitems from one team to another following these steps.
Go to Release > Planning > Team Scheduling.
Click the plus sign (+) next to the team currently owning the workitem you want to move to display all workitems assigned to the team.
Select the item you want to move and simply drag and drop it onto the team to which it is to be reassigned. The system adjusts cumulative counts and estimates for both teams.