Source : Webster's Revised Unabridged Dictionary (1913)

Reconfirm \Re`con*firm"\ (-f?rm"), v. t. [Pref. re- + confirm:
   cf. F. reconfirmer.]
   To confirm anew. --Clarendon.

Source : WordNet®

reconfirm
     v : confirm again; "You must reconfirm your flight reservations"