This is an irregular verb. It follows the conjugation pattern of the verb chegar.
Present:
O Lucas desliga as luzes antes de sair.
Lucas turns off the lights before leaving.
Preterite:
A Ana desligou o celular durante a reunião.
A Ana desligou o telemóvel durante a reunião.
Ana turned off her phone during the meeting.
Future:
(Eles) desligarão tudo à meia-noite.
They will turn everything off at midnight.