As far as I'm aware, Ren'py does not have a default key map set for quick save (I couldn't find it in the default key map list) and I didn't set one. So I'm afraid I don't think there is a key bind for the quick save function.
As far as resetting the game - there is no simple way to do this. I've never done it. I have heard about people doing it. You can google things like "How to reset a renpy game on steam" and find various threads giving instructions.
Typically it goes like this:
For Steam, Ren'py progress will be saved in two possible places. One is the Ren'py folder in appdata. If you navigate there and find a Gilded Shadows folder, look to see if there are any save files or "persistent" files you can delete.
But you'll also have to check in steam's files. If you right click the game in your launcher, you should see the option to manage the local files. In the game folder, there should be a "saves" folder that has all the save files in it, and a "persistent" file.
These will need to be deleted as well.
Again, I've never used this method to try to reset a game, it's just the information I've personally found. There is no simple "reset" button unfortunately.
I hope this helps and sorry you're having an issue with the quick save. D=