I bet you can reset it, but I don't know if you can do it without resetting everything else as well. The Tesla does have a "factory reset" option that I suspect will clear the pre-conditioning, but you'll also have to reset everything else as well.
As for the feature itself, it's an absolutely abysmal implementation, I recommend everyone turn it off. Tesla really tried to over think this one, and in the process ended up with a much worse implementation than if it had been much simpler. Right now the auto pre-conditioning only works if you have a very consistent schedule, and if that's the case, it would be dead simple to set it manually using a scheduler, set once and forget. This method would be more reliable, and also have the benefit of letting people without the consistent schedule enter when they wanted it as well. Over thinking this and making it automatic made it a useless option for the majority of owners.