Here is the USB connection on the PCB.
The labels say G D+ D- V
The idea is to cut the RJ connection off the end of the cable and solder the wires to those points.
Tie a knot in the cable too to add some strain relief so you don't accidentally pull out the wires.
I have no idea how the cable is wired internally or if they're all wired the same (so that everyone can use the same color code), so the safest thing to do is use a multimeter to confirm for yourself per the USB spec: