<<"Do trains stop at such small stations or is there any other alternative to inform in advance requesting a stop? If yes, how do we go about it?">>
The timetable will tell you.
I just checked the online timetable, and it shows the bus connections. 3 per hour.
It also shows train connections once per hour at xx19. Once per hour is common for small local stations. Also, the full printed timetable shows that a local train stops once per hour at xx19. It is a regular stop, and does not require any signal.
Also, at the station, on the wall somewhere is always a list of departures and arrivals for that station.
Train departures are usually on a yellow poster, but not always at small stations.
If there is no such list, then there will be a list at the bus station of the bus schedule.
You may be thinking of the the practice that, at some small stations, local trains will only "Halt on Demand."
In German - "Halt auf Verlangen."
If that is the case, there will be a sign and a button to push.
Also, on board the train, there will be a button to push, marked to show its function.
The trains that bypass Ringgenberg are express trains.