What have you tried so far?
Normally 4 people booking together will be placed together. Especially since you booked this so early. Most people that will be on that train have not even bought their tickets yet. So placing you together should have happened automatically.
But somehow you got assigned priority seats, and there were no 4 of those together. Did you request priority seats?
There is normally no way to modify reservations, as this is a train, not a plane. You can even travel on that train (within Switzerland) without reservations. I would suggest that since Sep 10 is ages away to just let it rest till you are here, and then sort it out at a station.