When you open the file, you will find 4 different setups: Houses, one-building blocks, single-family houses, and a highway.

You can change values and settings in the Modifier tab. The Vertex Groups in the Modifier tab cannot be changed there, as they have to use the already selected groups. You can assign different groups to vertices in the Vertex Group tab to design your city.

Performance may decrease, especially in larger setups, so consider enabling PerformanceFriendlyInViewport. You can also click the small TV icon in the Modifier tab to hide the assets and only display and move the vertices.