Hi, I'm French, and I am new on BTT. I would like to know where can I download the default preset for the Touch Bar and if there is a preset to switch easily between 2 preset(for me the Aqua and the default preset).
Thanks and sorry for my English if it's bad 
There is no default preset, if you mean the system touch bar - you can use the predefined action "Toggle BetterTouchTool Touch Bar" to switch between the system and BTT Touch bar (assign to a keyboard shortcut)
You can briefly tap fn or hold the apps button on AQT to switch to the native macOS TouchBar.