Hi.. I have an application with three activities, main, sc1 and sc2. I want to use a bottom to change between sc1 and main without to start activity "main" (similar to back action)
I would encourage you to move away from using multiple activities and switch to using "classes" see my post here https://www.b4x.com/android/forum/posts/342902/
This avoids "switching" between activities and having to recreate activities and mess with saving "state".
It also opens the door to using a drawer and a common toolbar with multiple "activities". Classes are also reusable so you could in effect have duplicate "activities" for example a web browser with multiple "tabs".