Wii U's optical drive is locked to the system itself. Like others have said, to swap the drive requires you to re-use the old logic board. Of course if logic board is the faulty part then Nintendo repair is the only option.
That being said, there should be screws on optical drive that you can took it apart to get the disc out.
That being said, there should be screws on optical drive that you can took it apart to get the disc out.