Do I have to throw away bitter eggplant after I have baked it? Can something be done or do I have to throw it away?
As already baked, I don't think so, it is possible to remove the bitterness. But you can make a curry (check some Indian recopies) with baked eggplant. It may help.
To avoid this problem in future: Cut the eggplant in a salty water. Then drain it and bake it. Salt water will reduce its bitterness.
[edited based on the comment. Thanks Stephie]