how to reassign the active task to some user using process model if I have tp id

There is a smart service (Task Smart Service plug-in) that allows you to reassign task to other users based on tp!id.

How do you want the re-assignment configured? You could configure the task to re-assign based on an escalation timer.
forum.appian.com/.../Escalating_a_Task

Also, here's a link to the component Sathya mentioned if the escalation timer is not what you are looking for: forum.appian.com/.../apps