Whether Tribunal has power to rectify / amend the orders passed by it

Yes, Tribunal may amend any order passed by it under in terms of Section 113(1) so as to rectify any mistake apparent from the record. Tribunal could undertake rectification on its own or on application by either of the parties to the appeal. The application for rectification shall be made within a period of three months from the date of the order sought to be rectified.
However, no amendment which has the effect of enhancing an assessment or reducing a refund or input tax credit or otherwise increasing the liability of the other party, shall be made under this sub-section, unless the Tribunal has given notice to him of its intention to do so and has allowed him a reasonable opportunity of being heard.

(ICAI FAQ PUBLICATIONS 06-09-2017 ORDERS OF APPELLATE TRIBUNAL: FAQ NO. 53)