Once you update the Status of a Work item to Completed, it will move off your work list or work board and onto your Completed board.
You can easily access all your Completed items on the Completed board.
There are two ways to access the Completed board.
Work List
Click the Completed button or Check icon on the header.
Use the Date Range Selector drop-down and select Completed Date.
Work Board
Time Flow - by default, this work board has a completed column that is automatically hidden. To unhide and view the completed tasks, click the eye icon at the top of the completed column.
For the other work boards (Weekly Calendar, Status, Assigned, Process, and Due Period), you can also use the completed button or check icon on the header.
In all cases, Filters will show Completed. This automatically shows you all your tasks with the Completed status on your Work list.