You can edit a deal’s won time directly in the Detail View of that deal after clicking the pencil icon next to Won time under Details, providing the new information, and clicking Save. 

Another way to edit the deal’s Won Time is in the List View. To do this, you can go to the List View of your Deals tab and apply the Won time column. To learn how to add columns to your List View, click here. 
After you add the Won Time column, you can edit the date directly by clicking the pencil icon next to the Won time value, providing a new date, and clicking the Save button.