The easiest way to redscale a 35mm film also requires you to waste a full roll.
Luckily I had one from when my Meikai Mango camera popped open with a full roll inside. Damn £3 eBay purchase.
Firstly, pull out all the film from the roll you don’t mind wasting.
Then cut it off, leaving about an inch still attached to the actual canister.
Get the film that you want to redscale and tape the end of film hanging out onto the inch of film that’s hanging out of the canister you cut earlier, but flip the film over first as the main aim is to have a film that is flipped over inside the canister.
Take the two canisters that are now attached by the taped together film into somewhere dark (I normally just put my hands under a blanket in my bedroom).
Start winding your empty film canister so the film from the full canister is wound into the empty one. This has to be done in complete dark or your film will be exposed.
Once all your film is wound into the canister that started emptyyou can cut it off from the canister that is now empty. Don’t forget to leave an inch of film still attached to the now empty canister as you can use this for your next redscale film, without having to waste another roll of film.
One thing to remember when shooting with redscale film is that it needs a hell of a lot of light. Most of the photos I took with my first roll came out too dark but there were a few that turned out ok.