Thank you very much for your reply, when we say we learn something every day, I did not know about the "Automation" ! you taught me something very interesting ! thank a lot
The problem I met was when I was opening a new automation window in one ANA Track, in the window "Add a parameter" I was not finding the plugin ANA in the list as choice, only Volume, Mute, etc and when clicking on "Plus..." only two folders were available "Track FX" and "All CC", nothing else.
The solution was in fact so simple ! you must just open the folder "VST instruments" (where all the VSTs plugins are inside, the ones you use for your music) and find the good track where you want to change the cutoff (for example), and click on the "R" button (its color changes into green), then use the pen or trace a line to change the value as like you want in the automation track located to the right.
Perhaps it will help somebody else one day.
Thank again Bryan for your precious help.