It’s not a hub to hub migration tool. It just lets you change the location in your account that a hub and its devices are assigned to. Or that devices that don’t need a hub are assigned to. But the devices remain attached to whatever hub they previously joined.
Moving Devices Between Account Locations? (ST added a second “home” just for my TV in the new app)
Also, Samsung support has now changed their advice. While it is now technically possible to have two hubs on one location using the new app, they are now telling people not to do it, but to have just one hub per location. This is a change from January 2019.
https://support.smartthings.com/hc/en-us/articles/115002084806
Note: It is not recommended to add a SmartThings Hub to a Location with an existing Hub.