If the sacrifice is injured from the Rig-veda side, let him offer a libation in the Gârhapatya fire, saying, Bhûh, Svâha! Thus does he bind together and heal, by means of the essence and the power of the Rik verses themselves, whatever break the Rik sacrifice may have suffered.

In plain words: If a mistake happens in the Rig Veda part of the ritual, the priest should pour an offering into the household fire, saying 'Bhuh, Svaha!' This uses the power of the Rig verses to repair the mistake.