Case dosen't have USB 3.0 Cable

Solution
Case has 2 x USB 2.0 ports
Motherboard has 2 x USB 2.0 connectors (supports additional 4 USB 2.0 ports)

No need to connect anything to the internal USB 3.1 Gen1 connector as you have no ports on case for that. The rear panel of the motherboard has:
4 x USB 3.1 Gen1 ports
2 x USB 2.0 ports
Case has 2 x USB 2.0 ports
Motherboard has 2 x USB 2.0 connectors (supports additional 4 USB 2.0 ports)

No need to connect anything to the internal USB 3.1 Gen1 connector as you have no ports on case for that. The rear panel of the motherboard has:
4 x USB 3.1 Gen1 ports
2 x USB 2.0 ports
 
Solution
Either you buy a different case with usb 3.0 (which would be what I would do), use the external ports from your motherboard, or you can run a cable from your internal hookups out the back of the case and around to where you would use it (very ugly).