How to restore all the car thumbnails back to normal

I had the wonderfull idea of running the thumbnail generator for all the vehicles in the game to change the backround colour to black instead of white.

As you can imagine, it didnt go very well. How do I restore/reset all the thumbnails back to normal?

I tried doing what this post said to do, but when I go to vehicles only a couple of cars appear and the folders dont even contain any thumbnails in them.

Edit: I cannot upload the link to the post so there will be an image below

 

Open the userfolder through the launcher (it's the second option) and follow the instructions of nadeox's post. The userfolder was moved from documents to Appdata in 0.22.

 

Thank you so much! it worked