The Enigma machine worked reciprocally so that an identical machine with identical settings would, if fed the enciphered letters, show the deciphered letters on the lampboard. Hut 6 had Enigma replica machines that were logically identical to the machines that the Germans were using.
The Enigma machine worked in a way that if you fed it the encrypted message, another identical machine with the same settings would show the original message on its lampboard.  Hut 6 had machines that were exact copies of the German Enigma machines.