引用自 Nem：

I got this quest I cannot for the life of me figure out how to complete it. I have pacifier enough minor factions to have different races. However, their population goes to random cities and I canot forcibly move them to one city. How am I suppose to complete this quest?

Open your city screen
Click on the population growth bar at the top
Click on the type of pop you want to grow.

See if that works

That will work, problem is, they mean particular city and do not mention which one. Sometimes it's mentioned in the dialogue (you can replay it in the Quests screen), but in this case I don't think so. So just to be safe, check how many different pops you have already for the quest on the tracker and grow new ones in every city matching that amount.