Question about fixing broken textures

Hi, I'm trying to fix an old map to make it work in 0.35. I managed to repair some things, however I can't find how to repair the terrain texture.
The terrain looks like this:

It should look like this:


Any ideas about how to fix / recreate textures for the terrain? Don't know if there's something to change in the world editor or if I have to modify certain files manually.
If it can help, here's how the folder of the map looks like: