When you conquer a city, it is initially "occupied" and will not grow. Assuming you want to keep the city, the only way to eliminate "occupied" status is to end the war in which you took the city on terms where you keep the city. One solution is to eliminate your enemy civ altogether (i.e., take all of his cities) -- when you take his last city, he is eliminated from the game, just as in Civ V. The other solution is to negotiate to keep the city in a peace treaty -- one of the items of value that you can obtain (or give up) in a peace treaty is to "cede" an occupied city to the civ that is occupying the city (or, alternatively, return an occupied city to the original civ). This is very different from Civ V, where you automatically kept cities you have already occupied during the war. So, in Civ VI, if you were at war with Pericles, and had captured (i.e., occupied) two of his cities (say, Sparta and Knossos), you could, in the peace treaty ask that he cede Sparta to you (plus give you gold, luxuries, great works, or other goodies), in exchange for your returning Knossos to him.