Twinmotion Decals

I am just a beginner with Twinmotion and I would like to use decals to create more realistic looking grass. In the below images I have used multiple Twinmotion stain decals to create some kind of dirtmap on grass field (150m x 150m).

Is it possible to somehow create my own decals in Twinmotion? For example replace the current stain decals with my own “dirt/stain” decal texture? I have also tried to find the folder location for these stain images but I have not found the location in my computer.