How to manually eject a disk

A disc or a disk?

pushing the eject key ejects the disk, holding it does a force eject (in some cases)

for manually ejecting the disc you must remove the MacBook Pro's base, Remove the disk drive (the mechanism in which the disc is loaded)

take apart the disk drive and remove the disk NOTE: YOU WILL WANT TO BE VERY, VERY, VERY ORGANIZED WHEN DOING THIS, THE DISK DRIVE CONTAINS SMALL PARTS AND IT WILL BE, REPEAT, WILL BE VERY DIFFICULT TO KEEP TRACK OF IF YOU ARE UN-ORGANIZED, also, there are very small screws.

If you damage anything, or even literally just remove the base, as far as I know, it will void your warranty, meaning AppleCare will not help you. I would directly contact apple support if I were you.