this whole time I've been assuming you have a Zenmuse H3-2D or H3-3D gimbal... do you? Those are the equipment I know well, and if you have one of those you can use the multicolor, 2 pair ribbon cable that was probably taped to the bottom of your phantom originally. it's 2 pair: a power/ground and video/ground. you'll need to patch these cables into the power and video cables that come with the transmitter.
Watch this video from about 1:15 to 1:45 you'll see what I'm talking about. He describes the cable thus: "the yellow and brown cable is your video out and ground... and red/brown is your live/negative that goes to power your transmitter" I've also included below a picture which should help.
so if you're NOT installing an iOSD mini, you can just patch directly to the inputs on your TS351 as thus:
Phantom ribbon cable yellow/brown pair: yellow will go to the Video In (yellow), and brown to the cam GND (black)
phantom ribbon cable red/brown pair: red goes to power in (red) and brown goes to power in (black).
So that's actually 4 solders
You can cut off the white and green "audio in" cables as you'll never need them, same for the VCC+ red cable
now if you do NOT have a Zenmuse gimbal, you'll still tap into power as I described above the only difference is you'll need a
GoPro live video cable like this one, and you'll patch the yellow / black of the cable directly to the yellow / black of the TS351 cable.