A really stupid question, but...

Don't you have to right click?
 
In Conquests (I think) there is a button in the top right hand corner of the Foreign Advisor screen that says 'More Civs'. Just click a civ other than yourself, click more civs, then select which civ you want to take the original one's spot.
 
You right click on a leaderhead, and a list will appear with the civs that aren't visible. Just select from there. (Or was it shift+right click)
 
shift-right click
 
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