Shujuettuex85 Hello,
Most TGV tickets are exchangeable, but you have to pay a fee and/or a surcharge if the new train is more expensive, depending of the conditions displayed on the ticket. If you bought the tickets on sbb.ch, call the Contact Center of the SBB with this number or visit a ticket office if you live in Switzerland:
0848 44 66 88 (24/7, waiting times may occur)
From a foreign country the number is: +41 51 225 78 56