Then it's a bit a bigger problem.
You can't add civs via the worldbuilder, but you can do it in another way, via a text editor (rightclick, open with wordpad/notepad).
If you do this and scroll down, you'll see different entries for teams and civs. Copy an existing entry, replace an "empy" one and change all the values to whatever you like, the civ you want, the leader, etc.
But then you have to add minimum a starting settler, and i'm not sure how to do it with the text editor. Try to find an existing entry for a unit, copy it, change it to a settler and change the owner, and when this is done, open the map normally with civ and place the cities and units there.