In the Task Center, you can manage your current as well as your archived tasks.
1. Click on the three stacked lines (
) on the far right side to enter the task center.
2. Ensure all filters are set correctly to show the archived task you would like to see. Select the Show Archived button. All of your archived/ deleted tasks will appear.
If for any reason you would like to unarchive a task, you can do this by selecting the blue edit pencil (
) on the far right of the desired archived task.
Click the Unarchive button.
Select the back arrow and click the blue Show Archived button to take you back to your active tasks. 
Click here for more information on How to Delete a Task.