Within Teamwork, you can change the creator of an individual task.
Go to the Tasks area of your project and select the task you wish you edit.
When viewing the task details, click the options button (three dots) in the top right and select Modify Properties from the dropdown menu.
In the modify modal, you can select a new creator from the dropdown. You can pick any user who has permissions to create tasks on the project.
Click Apply Changes to update the creator of the task.
For more information, see: Changing Completed Task Details