Reclaim

From DwarfFortressWiki

Are you looking to reclaim a lost fort? You may want to look at Reclaim fortress mode.

Reclaim is the opposite of forbid. Allows an item to be used by your Dwarves that has been forbidden, whether it's going to be hauled or used in construction. It's needed to use items found when you reclaim a fortress or build a fort near an existing settlement, as all items are auto-forbid.