Miss a connection

I have never missed a connection in Switzerland, even when the connect time was only 5 minutes. If you do miss it, there will be another train along soon.

I don't have Swiss train experience but I would expect that you would be able to use your ticket on the next train.

http://travel.thetrainline-europe.com/switzerland-trains/

Run like clockwork: InterCity trains leave often, at least
half-hourly, and are punctual enough to set your watch by. All trains,
boats, and buses are timed to connect with one another and so
connections across the entire country are perfectly timed to provide a
totally seamless journey. Many trains also feature panoramic windows,
allowing unspoilt views all the way up to the snow-capped peaks

I checked the schedule on SBB. Between Bern and Geneva there are two direct trains per hour ( unless you are traveling in April when there is construction on the tracks).

Can't you take one of those?

Even if you need to change at Neuchâtel, the schedule shows you come in on Track 2 and leave on Track 3, which is probably right across the platform.

Judy,
You do not reserve seats on Swiss trains. Your ticket will be valid on any train that day.
And, as Lola says, there are two direct trains per hour from Bern to Geneva, at 04 and 34 minutes past each hour. So you have plenty of choice.
I am not sure why you say you need to change trains, but even if you do 8 to 12 minutes is plenty of time.

That's why when we travel in Europe I ALWAYS breathe a sigh of relief when we arrive in Switzerland and can use the Swiss Transport System. I'm always on edge in Italy and France thinking when strikes, breakdowns or protests may pop up.