Instructions
Press "K" to open a dialog box with your skills listed.
Click the "Professions" tab.
Click the "Delete" button beside "Engineering." Confirm your decision when prompted.
Return to the engineering trainer who first taught you the skill. Relearn the skill as before.
Level up your engineering the same as before. When you reach the decision to pick your specialization at 200 engineering, select "Goblin Engineering" instead.