I don't know of anyone being able to do this consistently. I found no YouTube videos on it, either. I have attempted this unsuccessfully, since it is VERY easy to pull the coil out and disconnect it. And it is very hard to get fluval back into the carto in a way that 1) allows good contact with the coil, and 2) does not promote leaking. It seems the only way to do this well is to cut the tube at the base and pull it off the coil and filler, carefully unravel the filler from the coil, replace it with fresh filler, and slide the tube back on...and then seal it somehow.
Cartomizers are meant to be disposable, and are priced that way. I do clean mine by boiling them in water for a while, then drying them. This brings them back to fairly close to new in most cases. Unfortunately the classic old-style cartomizer, which is still one of my favorite vapes, never evolved to a more replaceable technology. Now many people who want something perpetually renewable go for bottom coil
tank cartomizers, like the Protank or Evod. One can pretty easily recoil these indefinitely, and they do not use filler, just a very short wick that is also replaceable. And one can
buy fully assembled coil heads for less than a cartomizer.
You might take this question to the Cartomizer subforum. They may have more tricks to do this.
Cartomizer Issues
Good luck!