Just noticed this notification regarding the RER C station for the Eiffel Tower:
"Warning, please note that renovation works will shut down "Champ de Mars Tour Eiffel" station (RER C) from July 15 (wednesday) to August 22 (saturday) 2015 and November 28, 29. Substitute buses will be established.
For more information : http://www.ratp.fr/en/ratp/c_21879/visiting-paris/ "
So, use the Metro -- either Trocadero or Ecole Militaire.