OK I was able to talk to William on WhatsApp and eventually got to the answer to my question. I'm not sure it's what you meant, but it's quite likely that you didn't know what my question meant either
So let me try to clarify my understanding in case it's useful to anyone else, and also to ensure it matches what you mean. Again, THANK YOU!
So, the video only talks about fishing one cable up. It's the trunk release one that you take the connector off before fishing it up. But if you look carefully in the video, when they actually fish upwards, there are two cables going up. That's because another cable also gets fished up - it's one with four bare wires. Both the parts that get fished up are from the main harness cable which is piece 8 in the attached image.
After you've fished up, you put the connector back on and attach that to piece 5 in the other attached image - the Trunk close button.
The 'mystery' part that I couldn't understand, was what they were the other fished cable (with 4 bare wires) to. The video is useless for showing that. But it turns out there is a part #9 that they don't even mention in the video, but which comes with the Hansshow kit. It's another piece with 4 bare wires on it, with plugs on the end. That part #9 is the mystery 'SOMETHING' that I was looking for. Since the video makes no mention of this and it just suddenly appears out of nowhere with them connecting to it, it was totally confusing.
So in summary, there are two different solutions for fishing up to the top. One cable you remove the connector from, fish it up, and put the connector back on. But the second cable (with four wires inside) has already been cut in half into parts 8 and part 9. This avoids needing to fish part 9 upwards! You fish up the cut cable end from part 8, then you tape it back together with part 9! Phew
I'm ordering tonight !!