Within Teamwork, you can edit tasks via the tasks breakdown panel in the Dashboard section of your project.
Go to the Dashboard area of your project and select the Summary subsection.
The tasks Breakdown panel is located to the right of the Summary view, and shows the total number and proportion of active tasks that are assigned to each person on the project. You also have the option here to switch from a breakdown of active tasks to a breakdown based on estimated time.
You can get a more in depth view and the option to edit these tasks by clicking the Expand option at the bottom of the breakdown.
A quick view will open showing a list of the users along with the task lists on the project. In this view, you can click a task to edit its details and also assign to a different user.
You can filter which tasks are shown by selecting a user from the list to the left.
You can also switch between active tasks and estimated time here using the dropdown in the top left.
For more information, see: Bulk Editing Tasks via the Tasks Breakdown View