untrain

From un- + train.

untrain (third-person singular simple present untrains, present participle untraining, simple past and past participle untrained)

1. To reverse or undo one's training; to become less trained than before
   • 2009 January 14, Patrick Healy, “Where Ballet Is a Boy Thing”, in New York Times‎^[1]:

     The 11 girls […] are all trained dancers in real life who, for the purposes of "Billy Elliot," must untrain themselves for each performance and dance with two very left feet.

• urinant