I have saved a custom configuration over a stock one, how to I return to the original?

Go to your UserFolder/vehicles folder.
Open the folder corresponding to that vehicle, and inside your should find the .pc that has the name of the configuration you are talking about.
That's the one you saved. Either rename it, or delete it, to let the game load the original one instead.

 

Nope, wrong folder.
That's the game installation folder, you should never touch those files.

The UserFolder is where all your custom files go. It's by default located in Documents.
If you can't find it, use the Launcher > Manage User Folder > Open In Explorer feature.





Since you modified one of the game's actual file, it may not work right if you try to simply put the file you removed inside. In that case, delete the ZIP and let Steam download the original file again: https://support.steampowered.com/kb_article.php?ref=2037-QEUH-3335