Hi @hopialikeit, although the Flash2 is a very capable shooter, it does not have manual setting for the shutter. You need a slow shutter speed to get this result.
Try to "Night" Scene Mode in the stock camera or my recommendation is to install Camera FV-5. This has shutter settings the stock camera is missing. You can download it for free from the Play Store and buy the Pro version to unlock some more features.
Another thing to remember is to keep the device steady when shooting with slow shutter speed.