Take your time and watch a lot of videos.
unlike metal welding, the plastic must never ever be moulten, just soft & sticky.
Try it on a few old buckets or =broken toys, it is a lot easier than most think.
If you use a soldering iron, it MUST BE REALLY CLEAN as the tacky plastic will pull the old solder / flux / corrosion debris off the iron and then it is all over.
