In the image the soldering and how it maps to the pads on the PCB are shown.

The GND can be connected to the large copper area. Just scratch away a bit of the green isolating layer. A bit of flux helps.

The soldering of the data lines is abit fiddly and rather for people with some soldering skills. Thin coil wire is a helpful.

In yellow the CC2 connection is shown. It requires a 5.1kOhm resistor to GND for correct identification by USB standard. The yellow rectangle represents the small SMD resistor.

If rotation of the cable is not needed, the data lines can be soldered to only the two 1DP and 1DN pins.

After testing, reassemble the whole keyboard. Thelast image shows how the USB-C fits into the opening.