I dismantled everything here to be sure, there is really only the antenna mounted and not the real TMC receiver. To open the adapter just unscrew the plastic tap and open the housing. If you only need to fix the cable connection at USB plug, you can skip demounting the adapter itself.

The flat cable consists of a white and a red cable, each shielded separately. Red = +5V, red shield = GND (0V and antenna GND), white = unused, white shield = antenna

Use a knife to open carefulle the micro USB plug along the line of the melded housing.

Desolder the white extra cable from the metal strip and open the clamp fixing the cable

Remove the plastic shortcut cover a bit to reach the soldering points and desolder the shieldings, red and white cable.

Shorten the antenna cable for a few centimeters and prepare the cables and shieldings to be resoldered to the plug.

Move the break protection and the plastic shortcut cover over the cable and resolder the cables and shieldings to the plug.

Close the metal clamp (Zugentlastung) and resolder the white extra cable.