The Assignee who Accepted a Task may assign another person to the Task:
See View Tasks to access Tasks.
Access the associated object Lifecycle page.
Approvals/Tasks display at the bottom of the Lifecycle/Review PowerView.
Use the check boxes to select your Task.
Click on the Approvals/Tasks page tool bar.
The Step 1 of 2 : Find People window displays.
Enter search criteria for a new person to make the assignee.
Click Find.
Search results display in the Select People window.
Use the radio buttons to select the person.
Click Submit.
The Add Comments window displays.
Enter Comments.
Click Done.
The Approvals/Tasks tab refreshes, showing the new assignee,