I am assuming you mean that after the form is submitted that is assigned to a user task and then you want it to be re-routed to a different user task? The only way to currently do this is to have a field value or an action button that would perform this from within the first user task.

The ability for someone to ad-hoc re-assign submissions to other tasks is posibbly coming in Forms 10 due out Q4 of 2015.