adb – How to downgrade the Google search app being recovered?

For some reason, I want to demote the Google search app (com.google.android.quicksearchbox) to an older version and upgrade it later on an Oreo Android 8 MI.
But when / system is mounted during recovery, I can not find the Google application in / system / app, although other system applications are present.
I do not want to root the device, so how?