I claimed an author challenge a few months ago, but have now decided that I'm no longer interested in writing a quiz on that topic. I've already abandoned the challenge, but is there a way to delete the quiz template? Or could I use the same template if I decide to write another quiz on a different topic? Thanks!

From the point of view of the editors, as long as the quiz has never been submitted, you can do whatever you want. If it has been submitted and rejected, please contact the editor who saw it to discuss options.

From the point of view of the challenge, I don't know what happens to that challenge. You want it to go back into the pool so someone else can claim it, but I'm not entirely sure exactly what the mechanism is for doing that. I do know that it's possible, and not difficult.

If you've already abandoned the challenge, someone else can already claim it. Agony's right-- just use the template for whatever you wish; it can always be moved to other sections.