You can decide the Home dashboard first. if you want to go with S2 to "M" directly then create action in s2 dashboard and target "M" dashboard.
else want to go S2 to S1 then create action in S2 Dashboard and add target as S1.
Thanks for the reply, but let me explain more,
during runtime of this Tableau Workbook, when the user finally land on Dashboard "S2", there's a possibility that he landed here navigated from Dashboard "M" or from "S1", so as a Developer/Designer I need a way to know this information for sure, then I can design my Back button in Dashboard "S2" to direct him exactly to his previous step, and I don't want to put 2 Back buttons, I need only one but clever enough to direct him back to the right Dashboard,
is this more clear now ?