Quest Finder is off by default and can be enabled through the Options Panel (press Esc to access your Game Options).
When you press the Quest Finder Button in your Journal (it's on the last page of your quests) The Quest Helper arrow will now point to the nearest available quest. It will start with the current zone you are in, then expand to the current world you are in. If it doesn't find any quests in that world, you will need to move to another world and press Quest Finder again.
When you use Quest Finder, a window will appear telling you where to go and who to talk to, and the Quest Helper arrow will now point to that location.
The quest tree is here... you might want to keep it handy since KI doesn't seem concerned and is just promoting the quest finder (which does not guarantee the main storyline quest). (You can always decline all side quests right now and that will help. Main storyline quests cannot be declined)
When you say, "gone not there I can't get it back" do you mean the main quest is no longer in your quest book?
Often, a newly given quest will replace an older one as the active quest, but all you need to do to get the original quest back is to click on your quests tab and click on the quest you want to make active.
Is it just that a new quest has been made active, or can you not even find the original quest in your quest tab at all? If this second situation is the case, submit a bug report to KI, via the Help button in-game.