In which game?
In Gen IV: D/P/Plt: Give it to the fat guy in the house in south-west Pastoria city. HG/SS: Give it to the person in the left side of the house in move house in Blackthorn city.
In Gen V: Give it to the remembering girl in the move house in Mistralion city.
More on Move re-learners: http://bulbapedia.bulbagarden.net/wiki/Move_relearner