Use once as a free action: if your rook still stands on its home square (h1 for white) and your knight on g1, they swap places.
You draft Country Auction in either mode. Free action: you choose when to use it, and it resolves without costing your turn.
As a item card, it is a one-use consumable, drafted in either mode.
“Sold: one slightly used tower, to the knight in the corner.”