Flight
Fly into Roissy Charles de Gaulle (CDG) or Orly (ORY) airport. You can take the train to Tours directly from CDG or take a taxi or the RER/metro into Paris from either airport and then the intercity train to Tours (see train Paris-Tours). Can also rent a car directly from the airport and drive to Tours.
Train
Intercity train from Gare Montparnasse/CDG to Tours train station. You can reserve tickets through the link.
Travel Note
Suggest to check the above site before leaving just to be sure!