To connect via BT, you need to create a BT port on your PC, and then select that port on the BT tab in the Mobimouse app on the PC.
There are instructions for doing that available at MobiMouse Instructions
Right-click on the Mobimouse icon in the system tray and select the "Help" option on the context menu to go to the setup instructions.
You can also access a link to those instructions from the BB mobimouse app on the right-click menu - select Instructions. But it's easier to view on the PC.