At a presentation in Paris on Friday, they announced that the Six Hours of Fuji had been brought forward to 14 October 2018.
BBC Sport reports that the move was officially requested by Fuji but the track is owned by Toyota, so it effectively comes from Alonso's team.
According to a report on Reuters, Alonso wants to win the Le Mans 24 Hours endurance race in France as part of the “triple crown of motorsport” achieved only by the late Briton Graham Hill.