We are staying in Grindelwald and thinking of this gor one day. Not sure of directions
I can help. :-)
I would take the cable car up to the Schilthorn in the morning. Then, you can take the cable car all the way down to Stechelberg. From there, you can either walk (about a half hour) or take the bus (# 41 direction Lauterbrunnen) to Trümmelbach Falls. After the Falls, you can walk or take the bus (# 41) to Lauterbrunnen. From there, train back to Grindelwald.
The SBB app or website can help with the times.
Thank you for the detailed directions. I really appreciate it