When fields are archived, they are automatically hidden from the farm map and fields list.
Web
Go to the Fields tab
In the filters dropdown menu, toggle 'Show archived fields' on
Archived fields will show at the bottom of the fields list and on the map
Mobile
Select the Fields tab in the bar at the bottom of the map
Tap 'Filters'
Toggle 'Show archived fields' on
Archived fields will show at the bottom of the fields list and on the map