You should not be worrying. You cannot imagine how efficient our public transport is until you have experienced it yourself.
It is a small station, and everything is well-signposted. In fact, it has the biggest panels I have ever seen in a station. Grindelwald, Wengen, and Lauterbrunnen are all very popular tourist destinations, and there are often hundreds of people changing trains.
Interlaken Ost The station has two underpasses, one with stairs, one with an incline plane (ramp).
When you arrive at Platform 2, simply make sure you are going to board the right train, watch out for the destination indicated on the coach.