Here is a schematic drawing:
You need to cut the V+ line (red cable) and extend the battery side to the switch (middle pin). One of the outer pins needs to be connected to the cut V+ line (transmitter side) and to one of the LEDs anodes. The other pin needs to be connected to the 2.4GHz module V+ line (in my case it is a red cable, but please refer to the FrSky manual for that) and to the second anode of the LED.
The ground (GND) line needs to be split. One cable has to be connected to the 35MHz module (existing line [black]), another one to the 2,4GHz module GND (in my case it is a black cable, but please refer to the FrSky manual for that). Also you need to connect the LEDs cathode to GND.
Thats all for the power supply of the modules
Last thing to do is to mount the antenna connector. Therefor you need to drill a hole (should be 7mm as per manual, but just check before
).
This is the easiest part, drill the hole, put the connecter in, fix the screw, mount the antenna.