Reddit reviews CESS 3.5mm Stereo 3-Pole (3-Pin) TRS Plug Jack Socket Adapter Cables Connectors - 10 Pack

I'm unsure about the quality of that soldering iron so hopefully someone else can give you advice on that, but I recently did a mod on my superlux hd688b's where I replaced the male jack with a female jack, so that might be something to look into. For soldering, look at tutorials online or just on youtube, and I would suggest to practice making good connections with the wires onto the jacks before you do the real thing. Make sure you fully heat up your surface and the wire to by putting the tip on it and holding it there, then bring the solder to it and let it flow around the connection. Here is a wiring diagram for a 3.5mm male jack. If you have trouble identifying what to connect where, look for a common wire that connects to both speakers on each side, and that will be your ground. Feel free to ask for some clarification on anything, I know this response is kinda all over the place lol.

Can't you just replace the aux port, like the actual port? im guessing its just wires that go into your head unit which can be easily replaced yourself