A Saver Day pass is not a ticket for a particular train. It is a public transit pass, good for all of Switzerland.
So even though you selected a particular train during booking what you bought was not a train ticket, but a pass good for all public transit for a whole day. You were offered that because at the time of purchase it was the best option.
So there is no need to change anything,
You probably also have a separate ticket for Chamonix to the Swiss border (as the Saver Dau Pass is not valid in France) and that ticket is also just valid on the next train as well. Train tickets are for a route, not a train. So just get on the first train you can when you arrive.