Thanks for the answer.

But when i start odoo with openupgrade i launch it from Openupgrade or from odoo ?

This link may help https://doc.therp.nl/openupgrade/migration_details.html

Would you explain please how to Edit the configuration files and command line parameters to point to the database you are going to upgrade

Take a look at this script which is a part of the openupgrade code. It was written to create a test db. Don't use it as is but you can create something similar that is specific to your environment.

https://github.com/OCA/OpenUpgrade/blob/12.0/scripts/create_test_db