Before data can be retrieved from the device via USB cable, device needs to receive the data collection profile settings first. There are two options how to do this:

Transfer settings via multi sync Android tablet 

Follow these instructions. After the first sync make sure to disconnect the device to prevent it from further Bluetooth syncing.

https://www.fitrockr.com/help-center/use-fitrockr-hub-for-multi-device-sync

Transfer settings via single sync smartphone 

Follow these instructions. After the first sync, disconnect device or log out of the app to prevent the device from further Bluetooth syncing.

https://www.fitrockr.com/help-center/use-the-fitrockr-hub-app-as-a-participant