After some careful examination of the camera I found the solution:
1-4 : there are 4 screws (2 left, 2right of the viewing lens) on the front (carefully lift the leather very slowly)
5-6 : there are 2 screws at the top sides (bottom near the back of the camera) (carefully lift the leather very slowly)
cover : you also have to remove the cover of the counter reset
When this is done , you can lift the viewing hood
then it is easy to remove mirror and ground glass