Plato relayed the story of Atlantis in his dialogues around 360 B.C. According to his dialogues, the city of Atlantis was an island located in the Atlantic Ocean.
The theory that Antarctica is Atlantis is a relatively new one, dating back to the mid 20th Century. According to Charles Hapgood's 1958 book 'Earth's Shifting Crust', the continent of Antarctica was in fact originally much further north than its current position. Due to the shifting of the Earth's crust, the continent was displaced, and the climate of the continent, which had been mild, plummeted to below freezing. This shift in location and temperature has led some to argue that an ancient Civilisation existed on the continent, which was subsequently destroyed by this monumental geographical realignment. In 2016, faint credence was given to this claim with the revelation that remains of a human settlement had been found under the Antarctic ice. One report claimed, 'the pictures, taken using remote sensing photography for NASA's Operation IceBridge mission to Antarctica, show what online sleuths believe could be a city.'
Charles Hapgood's theory was proposed before the advancement in research surrounding plate tectonics. As such, this specific theory regarding the location of Atlantis has largely been consigned to 'the fringes of Atlantean beliefs'. 
[P1] The shifting crust theory claims that Antarctica was once further north with a warmer, habitable climate. [P2] The shifting crust caused the continent to move south and changed its climate. [P3] Therefore there is the possibility an ancient civilisation is buried under the ice. This could be the Atlantis that Plato refers to.