Hello ada,
By default in the empty chunk the region has zero size and is located in the origin of the coordinate system (0,0,0). It can be automatically resized only if there are any sparse cloud points (i.e. aligned cameras) in the active chunk. So I can suggest to import the dense cloud to the chunk with some existing alignment, it will allow to modify the size of the bounding box in a more convenient way.
However, even when you press Resize Region button you would be able to see the corners of the box in the same location. You can use Move Region tool for better convenience, as it will show the coordinate system axis in the box location, thus attracting your attention.