If this person fell in love on their own, there is no spell to release a love. If a spell was cast upon them, then the spell must be said in reverse, a black candle burned while this is done, and the paper that the reverse spell is written on should be burned in the fire and left to smoke until it stops on its own. Everything must be cleaned afterwards, there can be no trace of the spell ashes, and the candle must be burned until it burns itself out, then the stub thrown away.