Within Teamwork, you can quickly edit existing task descriptions.
When viewing tasks in list view, click the more link to the right of the task name to expand the description.
Hover over the description area and click the edit pencil on the right to update the description.
When viewing the task details view for an individual task, hover over the task description area to reveal the Edit button. An inline editor will open allowing you to quickly update the text.
For more information, see: Quickly Adding Tasks from Highlighted Text