Within Teamwork, you can edit tasks from the tasks breakdown in the overview section of your project.
Go to the Overview section of your project and select the summary section.
You will then see the option for breakdown on the right of the summary section.
The breakdown 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.
When 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 near the top left.
For more information, see: Bulk Edit Tasks via the Tasks Breakdown View