[O] Org-mode and koma-script

[gmx]

Hello,

I'm trying to use the koma class. I found a configuration of the.emacs 
file, in the manual and in a Stack Exchange post 
(https://tex.stackexchange.com/questions/364914/using-koma-script-article-with-org-mode). 


I open a new .org file, and I declare:
#+TITLE: MyTitle
#+DATE: date
#+LANGUAGE: fr
#+LaTeX_CLASS: koma-article

When I want to export my work in .pdf, I get the following answer: 
Unknown LaTeX class 'koma-article'.

What to do?
Thank you for your advice

Frédéric (real newbie with org-mode, but I do my best)