From Archon Arcana - The KeyForge Wiki

If two game elements are swapped, they exchange places with one another.

When two creatures are swapped, they exchange positions. This means that each takes the position in the battleline of the other. The two creatures swapped must always be controlled by the same player. If cards from two distinct game areas are swapped (such as a card in play and a card in hand), the cards switch game areas.

Official rules v1.8 March 2021