I looked in the config files and there is no option to change the skin type

How do I change it?

I looked in the config files and there is no option to change the skin type

How do I change it?

If you are talking about swapping between Steve and Alex model, there isn't a config file for it.
Instead, this mod will detect which model by checking provided skin's arm width
You can simply use this app to convert between steve/alex model.
https://util.gflash.eu/mcskinconverter/

have you found a solution?